Develop Reference

How to handle timezone difference

I have my aplication which uses BST time zone(UTC+1) and another application where i am using the value from the above specified application . On my second server the timezone is UTC.
Because of this when i get value in a datetime property there is a diufference of one hour and because of that the value is going wrong.
I wont be able to adjust the timezone on both the servers . How can i convert the value to a BST time zone in my second application using .net.
public DateTime? EmploymentStartDate { get; set; }
This is my property in my model.
the value from my first server is 29/8/2001 00:00:00 when it comes to the second server where the timezone is UTC it is 28/9/2001 23:00:00 .

It's simple, you must consider all the DateTime always in UTC, so simply call ToUniversalTime() to convert every instance in UTC timezone:
DateTime dt = DateTime.Now;
dt.ToUniversalTime();

I agree with Daniel A. White. You should store everything as UTC and convert the date to local date on the client.
Look this https://msdn.microsoft.com/en-us/en-en/library/system.timezoneinfo.converttimefromutc(v=vs.100).aspx

private DateTime? _employmentStartDate;
public DateTime? EmploymentStartDate
{
get
{
return _employmentStartDate != null ? TimeZoneInfo.ConvertTimeFromUtc(_employmentStartDate.Value, TimeZoneInfo.Local) : new DateTime();
}
set
{
_employmentStartDate = TimeZoneInfo.ConvertTimeToUtc((DateTime)value);
}
}

Also consult this previous StackOverflow post:
Should MySQL have its timezone set to UTC?
This article (and the numerous other articles and web-pages that it links to) discusses MySQL, but the concerns and techniques are similar for any database and programming language.

While your (the OP's) question seems to be about how to convert time information between time zones, the discussion in the comments has grown hot on the subject of choosing a format for storage. First things first – to convert your UTC time to BST you can use TimeZoneInfo.ConvertTimeFromUtc. This method “converts a Coordinated Universal Time (UTC) to the time in a specified time zone.”
Here’s an example:
var bstZone = TimeZoneInfo.FindSystemTimeZoneById("GMT Daylight Time");
bstTime = TimeZoneInfo.ConvertTimeFromUtc(timeUtc, bstZone);
NB 1: If what you really want is local time on the server when executing, obviously you should rather use ToLocalTime(), and that will yield the same result if that local time happens to be BST (and the Kind property of the DateTime variable is not DateTimeKind.Local).
NB 2: To the best of my knowledge, the TimeZoneInfo class referrers to "British Summer Time" as "GMT Daylight Time", and I’m assuming that’s what you refer to as BST. But don’t take my word for it – you need to make sure yourself that you have the right time zone ID.
Now, about storing:
TL;DR
A time signature without time zone information is unreliable information. Given this premise, there is however no true “right or wrong” time zone to use for storing. While most people might argue that UTC is to be considered a best practice, first of all that information (that it's in UTC) should still be stored explicitly alongside the timestamp, and secondly, there may be practical reasons why another format is preferable in a specific scenario.
When performing arithmetic calculations on time values you should use universal time representations to avoid hiccups with regard to daylight saving practices and such.
Be weary of complications that might arise from serializing and de-serializing mechanisms making the wrong assumptions about the information you provide, e.g. System.XML.Serialization or a database engine.
Obviously, when presenting your time information (that is, when creating a string representation suitable for interpretation by humans), you should do so in whatever format the user should be expecting. Regardless of how you persist your values, conversions (with offset) may be necessary to do so.
Check out these links for more information:
Converting Times Between Time Zones
Coding Best Practices Using DateTime in the .NET Framework

CRM 2011, Date in plugin and DST

I have one issue which I resolved by myself but yet need some confirming words whether I am 100% correct on my thought, just because there is not any documentation I found to prove myself correct.
My server is in DST time currently, CRM UI is also showing 1 hour up then data stored in db. that's fine.
When I calculate and store date with plugin, after my plugin update operation finishes, CRM platform deducts 1 hour from data I saved. I have read that when we do some operation via SDK related date time, CRM stores date time as it is. is it the case that when time is in DST, platform also get involves to deduct 1 hour by then ?
As a resolution, I have commented out my line of deducting 1 hour and letting CRM to do it now.
Am I correct on my understanding or it would be appreciable if some one can provide any documentation URL.

Any time you're working in the SDK, DateTimes are retrieved and stored as UTC. The CRM web platform will convert the UTC time into the user's time. You shouldn't need to be doing any Conversions of time, just using UTC.
Let's assume your local time is UTC -1 (with DST since UTC doesn't observe it). So if UTC is 14:00, your local time is 13:00.
Let's also assume your plugin in going to populate a date attribute on the entity that is for the current time, tomorrow. If your code looks like this:
entity.new_SomeDate = DateTime.Now.AddDays(1);
service.Update(entity);
Assuming DateTime.Now is 13:00, it'll store 13:00 in the database (as if it was UTC). Then when you go to look at the time value from the CRM website, since you're UTC - 1 it'll display 12:00, even though you wanted 13:00.
Now if your code looks like this:
entity.new_SomeDate = DateTime.UtcNow.AddDays(1);
service.Update(entity);
Assuming DateTime.Now is 13:00, it'll store 14:00 in the database since DateTime.UtcNow is 14:00. Then when you go to look at the time value from the CRM website, since you're UTC - 1 it'll display 13:00, since it'll take the UTC value - 1.
Now if your code looks like this:
entity.new_SomeDate = entity.new_UserEnteredDateFromCrm.AddDays(1);
service.Update(entity);
The new_UserEnteredDateFromCrm will already have been converted from the users' Time Zone to UTC and it'll work as expected.
This makes DateTimes that you would prefer to store as Dates very difficult though (birthdays anyone?) and you may have to think through it a little more in depth.

I've figured it out myself. that date has component in it which explores what kind of date time is it in. it can be either Utc, Local or Unspecified.
when you pass any date to CRM attribute via code. make sure that date time kind is Utc, otherwise CRM service internal operation will convert it to be into Utc.
In my case, I was stucked to this because when I read date from CRM, I had to set office start in that date. e.g. I needed to make 03/02/2014 12:00 to 03/02/2014 8:30 to make incoming date aligned with office start time. I was doing operation like,
DateTime InDate = Case.CreatedOn.Value;
DateTime Dt = new DateTime(InDate.Year,InDate.Month,InDate.Day,8,30,0)
Having InDate in Utc Time, I was creating new date object so it lost DateTime kind from Utc to Local ( having in DST it signifies to be 1 hour up)
to avoid, always set DateTime kind to be exactly as provided In date to new object. e.g. above operation can be done alternatively like.
DateTime InDate = Case.CreatedOn.Value;
DateTime Dt = new DateTime(InDate.Year,InDate.Month,InDate.Day,8,30,0)
Dt = DateTime.SpecifyKind(Dt,DateTimeKind.Utc)
Hope that Helps.

Comparing time regardless of date

I have an object that has properties currently as DateTime.
The object is marked as valid within a time frame. The default being 00:00:00 to 23:59:59
The user enters the value in the UI and the property is set via:
new DateTime(DateTime.Now.Year,
DateTime.Now.Month,
DateTime.Now.Day,
model.Hours,
model.Minutes,
model.Seconds)
This is then converted to UTC when it hits the database.
Today's date is 29th August 2013. If a colleague in India runs this program it will store the data in the database as 28th August 2013 18:30:00 as they are 5.5 hours ahead of UTC so 29th August 2013 00:00:00 becomes yesterday.
When the logic tries to determine if the object is valid the logic is:
if (DateTime.UtcNow.TimeOfDay > model.MyPropertyFromDB.TimeOfDay)
We are trying to determine if the current time is within a range of 00:00:00 and 23:59:59
This fails as 14:00 (current time) is not greater than 18:30
What would be the best approach to compare just times?
Would storing the values as DateTimeOffSet help, is using ToLocal() ok?
Other considerations are that a user in India is using the app which is hosted in the UK so it needs to be timezone aware.
Thanks

Like others, I'm still unclear on exactly what you are wanting. But clearly, you shouldn't do this:
new DateTime(DateTime.Now.Year,
DateTime.Now.Month,
DateTime.Now.Day,
model.Hours,
model.Minutes,
model.Seconds)
That would be much better as:
DateTime.Today.Add(new TimeSpan(model.Hours, model.Minutes, model.Seconds))
But why are you doing this to begin with? Either of these would give you back the local date. I assume this is going to run on a server, so do you really want the time zone of the server to influence this result? Probably not. Please read: The Case Against DateTime.Now.
If you wanted the UTC date, you could do this:
DateTime.UtcNow.Date.Add(new TimeSpan(model.Hours, model.Minutes, model.Seconds))
That would at least be universally the same regardless of your server's time zone. But still, I don't think this is what you are after.
What's not clear is why is the user only entering the time while you are assigning the current date. If the date is relevant, then shouldn't the user enter it and it would be part of your model?
If the date is not relevant, then why are you storing it? You can use a TimeSpan type for the time value internally. You didn't say what your database is, but let's just guess that it is SQL Server, in which case you could use the time type on the field in the table.
I suppose it's possible that the date is relevant, but you want to control it, while the user takes control of providing the time. If that's the case, then you must know the time zone of the user (or the time zone of whatever the context is if it's not the user). Assuming you had a Windows time zone identifier (see the timezone tag wiki), then you could do something like this:
var tz = TimeZoneInfo.FindSystemTimeZoneById(theTimeZoneId);
var local = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, tz);
var dt = local.Date.Add(new TimeSpan(model.Hours, model.Minutes, model.Seconds));
If you don't have the time zone information, then this wouldn't be possible to solve.
As general advice, you might want to try using Noda Time instead of the built-in stuff. It's much better at helping you figure out this sort of thing. From the main page:
Noda Time is an alternative date and time API for .NET. It helps you to think about your data more clearly, and express operations on that data more precisely.
That appears to be directly the problem you are having here. If you want to clarify some of the questions I asked, I'd be happy to edit my answer and show you exactly how to do this with Noda Time.
Why your question is confusing
We are trying to determine if the current time is within a range of 00:00:00 and 23:59:59
All times are within that range. Well, maybe a value like 23:59:59.1 would be outside of it, but you aren't collecting fractional seconds in your model, so that's irrelevant. But why would you need to validate that? Maybe you are just trying to avoid numbers that aren't valid times at all? Like 99:99:99?
This fails as 14:00 (current time) is not greater than 18:30
Wait - you didn't say anything about comparing one time greater than another. 14:00 and 18:30 are both still in the range you specified.
What would be the best approach to compare just times?
Hard to answer. Are they both UTC times? Is one UTC and one is local? Are they both local? Do you know the time zone of the local times? Are you prepared to deal with ambiguous or invalid local times do to daylight saving time transitions?
Would storing the values as DateTimeOffSet help?
Perhaps, but you haven't given me enough information. It would help only if the date portion is relevant and the you get the correct offsets.
is using ToLocal() ok?
I would argue that no, it's not ok. Local in this context will give you the time zone of the server, which you probably don't want to introduce into your business logic.

So if I understand this correctly you have a time saved in UTC in the database and you are trying to determine whether it falls within a particular time frame? I'm not sure if you want the time frame in local time or UTC so here are both:
DateTime dbTime = model.MyPropertyFromDB;
TimeSpan minTime = new TimeSpan(0, 0, 0);
TimeSpan maxTime = new TimeSpan(23, 59, 59);
if (dbTime.TimeOfDay > minTime && dbTime.TimeOfDay < maxTime)
{
//Within time range (UTC)
}
if (dbTime.ToLocalTime().TimeOfDay > minTime && dbTime.ToLocalTime().TimeOfDay < maxTime)
{
//Within time range (local)
}
Edit: If you want to compare Now to a start and end time from an object in database:
TimeSpan now = DateTime.UtcNow.TimeOfDay;
TimeSpan startDate = model.startDate.TimeOfDay;
TimeSpan endDate = model.endDate.TimeOfDay;
if (now > startDate && now < endDate)
{
//Within time range (UTC)
}

I would say that the methodology being used here is fundamentally flawed and that you need to take a different approach.
new DateTime(DateTime.Now.Year, // Server date
DateTime.Now.Month,
DateTime.Now.Day,
model.Hours, // Local time
model.Minutes,
model.Seconds)
I can't see a way of 'normalising' the input in this way, unless you have a way of reliably knowing exactly which timezone a user is in. Simply, there's no easy way to turn a date built in this way into UTC.
My first question to you is, how is the model being passed from client to server? If you're using javascript/ajax then the solution should be fairly straightforward to solve by constructing the datetime object on the client (which will include their timezone data) and then rely on the browser to convert it to UTC for transit.
If you are using Razor\MVC then you can achieve a similar thing with forms encoding, except that you will need to call ToUTC on the server as the browser won't automatically fix the date for you for this media format.
Both methods require that you build a full datetime object on the client and then submit it, rather than trying to build it from seconds, minutes, hours on the server. You don't need to expose all this to the client of course, as long as the datetime is fully formed at the point of submission.
Once you've got a nice UTC datetime, you can extract just the time if you don't need the rest of it.
Hope this helps.
Pete

How to store my dates?

I don't have much experience with Utc Dates, but from what I know, they are in most cases the best way to store dates.
But I'm currently working on a program and I'm in doubt what will be the best way to store my dates. In the program, a user can follow a course for five weeks, starting on the day of registration. Every day he has to fill in a form, which is saved for that day.
Currently, I'm saving the StartDate and EndDate of the course as DateTime (no Utc) Should I save this as Utc, or isn't it necessary? Because I only need the day (if the user registers on February 8th at 10:04, all the system needs to know is that February 8th is the first day of the course. Is there maybe a better way to store this information? And what would be the best way to save system-event-dates (like user logged in, account created, etc)?
I used to store the form-data also with a DateTime, to calculate on which day it was submitted, but I changed it so it only saves the relative day-number (e.g. day 5).
Btw, I'm using C# and a SQL Server database.

UTC (Coordinated Universal Time) has to do with the time component of a date. It's a standard way to store DateTimes so that you can compare without worrying about timezones.
If all you are worried about is the Date Component & Timezone/Location is unimportant you could just store it in the database as 2012-02-01 00:00:00
You can get the date only component in .NET using
System.DateTime.Today;
Alternatively if you're working with some other Date...
DateTime dt = DateTime.Now;
dt.Date; // <--- this will give the Date Component with the Time stripped back to 00:00:00

Why don't you just store the dates in a DATE database column, and not worry about time zones at all?

Generally you want to store in UTC if there is a functional requirement for your system to be able to work with users in different timezones.
Let's say you have a user in Hong Kong and a user in Sydney looking at the same event. If you want them both see the event date (and time) in their timezones, then here we are, you will probably need to store it in UTC and then present to users respecting their geo locations.
If you don't have such requirements, you don't do such conversions and you only assume one timezone then you don't need to add more complexity into your system, just use Date column and store the current date there.
But if you do - go for UTC. In this scenario you will need DateTime, not just Date. This is because 21:30 in one timezone can be 2:30 next day in another timezone so time really matters.
When showing to a user you may convert it to the user's timezone and then throw time away, but in order to make the conversion correct you will need to keep time.
It is easy to work with UTC in .NET, DateTime has .ToUniversalTime() method that converts a datetime value to UTC for you:
var utcNow = DateTime.Now.ToUniversalTime();
there is also a property:
var utcNow = DateTime.UtcNow;
EDITED
Use TimeZoneInfo static class to convert datetimes from/to timezones you need (for example from UTC to the specified user's timezone:
TimeZoneInfo.ConvertTimeToUtc(...)
TimeZoneInfo.ConvertTimeFromUtc(...)

How to work with time zones in ASP.NET?

I am working on an "online reminder system" project (ASP.NET 2.0 (C#) / SQL Server 2005)
As this is a reminder service which will send the mail to users on a particular dates. But the problem is users are not from a specific countries, they are from all over the world and from different time zones. Now When I am registering I am asking for users time zone in the same way as windows asks our time zone at the time of installation.
But I am not getting the if the user selected (+5.30) or something timezone then how to handle this time zone in my asp.net application. How to work according to timezone.
And please suggest if there is any better way to handle timezones in this application ??
Thanks

First thing is to make sure which time zone your data is in. I would recommend making sure that any DateTime that you store, is stored in UTC time (use the DateTime.ToUniversalTime() to get hold of it).
When you are to store a reminder for a user, you will need the current UTC time, add or remove the user's time zone difference, and convert that new time back to UTC; this is what you want to store in the DB.
Then, when you want to check for reminders to send, you simply need to look in the database for reminders to send out now, according to UTC time; essentially get all reminders that have a time stamp that is before DateTime.Now.ToUniversalTime().
Update with some implementation specifics:
You can get a list of time zones from the TimeZoneInfo.GetSystemTimeZones() method; you can use those to show a list of time zones for the user. If you store the Id property from the selected time zone, you can create a TimeZoneInfo class instance from it, and calculate the UTC time for a given local date/time value:
TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById("<the time zone id>");
// May 7, 08:04:00
DateTime userDateTime = new DateTime(2009, 5, 7, 8, 4, 0);
DateTime utcDateTime = userDateTime.Subtract(tzi.BaseUtcOffset);

I would recommend to always use UTC (GMT) time on the server side (in code-behind, database, etc), and convert time from UTC to local time for display purposes only. This means that all time manipulations - including saving time in database, performing calculations, etc - should be be done using UTC.
The problem is: how does your code-behind know what is the time zone of the client browser? Say the user enters some date/time value (such as 12/30/2009 14:30) in the form and submits it to the server. Assuming that the user submitted local time, how does the server know how to convert this value to UTC?
The application can ask the user to specify the time zone (and save it in a persistent cookie or database), but it requires and extra effort from the user, and your app would need to implement the logic and screens for this. It would be nicer if the app could determine client's time zone automatically.
I have addressed this issue with the help of JavaScript's getTimezoneOffset function, which is the only API that can tell the server about the time difference between local time on the client and GMT. Since this is a client-side API, I did the following: on the server side check for a custom session cookie holding the time offset value, and if it's not available, reload the page (only during GET, and not POST, calls) with some JavaScript logic added to generate the time offset and save it in the cookie. From the client-side this is almost transparent (once during session I reload a page on GET). Once I have the offset in the cookie, I apply it to the time management functions depending on direction of time conversion (UTC to local time, or local time to UTC).
This may sound a bit complicated, and it is, but after I wrote helper functions, integrating this feature in the site was a matter of making a single call in Page_Load (of pages that needed time conversion), and using time conversion routines when sending and retrieving time values to and from the browser. Here is an example of how it can be used:
using My.Utilities.Web;
...
// Derive the form class from BaseForm instead of Page.
public class WebForm1: BaseForm
{
...
private void Page_Load(object sender, System.EventArgs e)
{
// If we only want to load the page to generate the time
// zone offset cookie, we do not need to do anything else.
if (InitializeLocalTime())
return;
// Assume that txtStartDate is a TextBox control.
if (!IsPostback)
{
// To display a date-time value, convert it from GMT (UTC)
// to local time.
DateTime startDate = GetStartDateFromDB(...);
txtStartDate.Text = FormatLocalDate(startDate);
...
}
else
{
// To save a date-time value, convert it from local
// time to GMT (UTC).
DateTime tempDate = DateTime.Parse(txtStartDate.Text);
DateTime startDate = ConvertLocalTimeToUtc(tempDate);
SaveStartDateInDB(startDate, ...);
...
}
}
...
}
If you need more specifics, check out the It’s About Time: Localizing Time in ASP.NET Applications article (sorry, but I do not have a direct link to the article on the publisher's site, since asp.netPRO restricts access to paid subscribers only; there are links to PDF copies, though). I wish I could post the sample from the article, but I don't want to violate the copyright; however, here is a project to build a helper library that has all necessary functionality and documentation (just ignore the stuff you do not need).
UPDATE: The article has been posted online with sample project by the new publisher here.

The problem with all of the answers so far is that they do not take into account what Prashant is trying to achieve. If the user of his system on the day before daylight savings changes has an offset of +12 and sets a reminder for the next day, his offset when the reminder is supposed to be triggered will be +13 instead.
That is why you can only use current offset for something that is happening now. Although I do agree with everyone else that all times server-side (except possibly those used only for display) should be stored in UTC.

You may want to look at using the DateTimeOffset structure instead of the DateTime if you are on framework 2.0 or later.
The DateTimeOffset represents a point in time relative to UTC time, so it should be easier to work with in this case.

There are 2 steps:
Detect different timezone at client side using Javascript:
var dt = new Date();
var diffInMinutes = -dt.getTimezoneOffset();
Then at server side, C# code to convert server time to client time based on detected timezone offset above:
------------------------;
string queryStr = Request.QueryString["diffInMinutes"];
int diffInMinutes = 0;
if (Int32.TryParse(queryStr, out diffInMinutes))
{
clientTime = serverTime.ToUniversalTime().AddMinutes(diffInMinutes);
}

Basically, all you need to do is add the offset (hours + minutes) to the local time that the user has entered. Adding in the offset basically gives you a DateTime in the UTC (basically GMT) timezone.
It's usually easiest to standardize all your times to UTC, so that your application logic doesn't have to deal with the offsets.
This page has a few good examples: http://msdn.microsoft.com/en-us/library/bb546099.aspx

The issue is that the offset from UTC will vary at different times of the year -- each time zone has its own rules. (I learned this the hard way when developing meeting room scheduling app.)
Looks like there is built-in support here: http://msdn.microsoft.com/en-us/library/system.timezoneinfo.converttime.aspx
Haven't tried it myself but it seems to promise the correct conversion, accounting for daylight savings.
If not, here is a (pricey) commercial tool I have used: http://www.worldtimeserver.com/time_zone_guide/