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DateTime.TryParse() not working with formatted date dd/MM/yyyy

This code returns (min time 1/1/0001 12:00:00 AM) not Date.Time.Now . Try Parse works for MM/dd/yyyy but not dd/MM/yyyy . Any suggestions
Here is code
DateTime start, end;
DateTime.TryParse(EPSDate12.Text, out start);
string TNow = DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss"); // Works
// string TNow = DateTime.Now.ToString();// works but gives MM/dd/yyyy as expected
DateTime.TryParse(TNow, out end); // No. gives min time (1/1/0001 12:00:00 AM)

Use TryParseExact and supply the format string.
Also examine the return value from TryParseExact to know if it failed or not (it returns a bool)
I see "EPSDate12.Text" which i suspect may be a TextBox: If you're doing this in a UI, make life easy and use a DateTimePicker - you can set the format, the user can type into them just like a textbox, but they don't accept invalid inputs, and all you have to do is get the .Value property which gives you a DateTime
As to why your attempts to parse the string you made don't work, I think it most likely that the date format Parse is using (which is based on the culture settings of the executing thread) is not the same format as the string you prepared using your forced format. Either make sure your forced format is matched to the current culture, or use a culture that matches your forced format, or use [Try]ParseExact to force the format for parsing like you did when creating the string
See https://learn.microsoft.com/en-us/dotnet/api/system.datetime.parse?view=net-5.0#Culture for more info

The datetime value is internally the same. But, ToString() return value, depends on
the local machine culture setup.
Reference article
The default DateTime.ToString() method returns the string
representation of a date and time value using the current culture's
short date and long time pattern. The following example uses the
default DateTime.ToString() method.
For en-US culture(MM/dd/yyyy hh:mm:ss) , it will be in
7/28/2021 11:37:40 AM
If you want to see in en-GB(dd/MM/yyyy hh:mm:ss), you can apply conversion as given below:
var culture = new CultureInfo("en-GB");
MessageBox.Show($"{DateTime.Now.ToString(culture)}");
28/07/2021 11:45:09 AM
you can also specify exact custom format, in which you want to display.
MessageBox.Show($"{DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss tt")}");
28/07/2021 11:45:09 AM

Thanks for suggestions . Yes DateTime.TryParse is not working and it could be format issue
This line of code.
string TNow = DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss");
generates
29/07/2021 14:49:03
which looks OK but fails TryParse

DateTime Format - Any System Datetime.now to "DD/MM/YYYY hh:mm:ss"

I have a program that do several things.
Two of them is read a date from a txt and rewrite a date in the same txt.
The read of the date is a regex expression like:
[0-9]{2}/[0-9]{2}/[0-9]{4} [0-9]{2}:[0-9]{2}:[0-5]{1}[0-9]{1})
The problem is that my regex expression only works in the format
"DD/MM/YYYY hh:mm:ss" and its impossible to make sure my regex expression can match all system datetime formats.
So, I need to make sure my program run's in every system, regardless the system datetime.now.
For that, i thought about format every system datetime.now, at start, to the format mentioned "DD/MM/YYYY hh:mm:ss".
At the moment i have the following code:
Datetime currentDate = DateTime.ParseExact(DateTime.Now.ToString(), "DD/MM/YYYY hh:mm:ss", CultureInfo.InvariantCulture);
However, when running some tests, using a system date in format "D/M/YYYY h:m:s" i get the error:
"String was not recognized as a valid DateTime."
The problem is that if my date, for example, is "9/27/2019 04:26:46"(M/D/YYYY h:m:s) it can't fit in the format i defined.
Any idea?
Thank you in advance!

You need to use the same format string and culture in every place where you convert the DateTime to string as well. In your sample code, you're doing
DateTime.Now.ToString()
This uses the default culture for the thread, and the default format. Unless assigned otherwise, the thread is probably using the local culture info. Instead, you would want to use the same format and the invariant culture:
DateTime.Now.ToString("dd/MM/yyyy HH:mm:ss", CultureInfo.InvariantCulture);
(note the lowercase "dd". "DD" is not a valid format specifier for date times; these things are case sensitive. Also note the "HH", which gives a 24-hour value, rather than 12-hour)
In practice, just using the invariant culture should be enough for persistence. Cultures already include default datetime formats, so unless you have a specific need to use a different format, why not use the default?
Also note that DateTime doesn't have a format. The format only comes into play when you convert from or to a string. That is the place where you need to ensure the same culture and format is used for both sides of the operation (and that's why for persistence, especially for data shared between different users or computers, you generally want to use the invariant culture).

If you need
to make sure my program run's in every system, regardless the system datetime.now
you can adapt international standard for this, say, ISO 8601.
In order to validate the DateTime, regular expressions like you have are not enough (just imagine leap years), but TryParse does it job:
string source = "2019-09-26T23:45:59";
// Either current culture date and time format or ISO
bool isValid = DateTime.TryParse(
source,
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeLocal,
out var _date);
Or if you want to be more restrictive use TryParseExact:
// ISO only
bool isValid = DateTime.TryParseExact(
source,
"s",
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeLocal,
out var _date);
If you want to represent DateTime.Now in ISO 8601, add "s" standard format string:
string dateAsString = DateTime.Now.ToString("s");
Alas, you can provide a bunch of formats which are able to cope with any date and time formats; a classical example of ambiguous date is
01/02/03 - 01 Feb 2003 (Russia)
01/02/03 - 02 Jan 2003 (USA)
01/02/03 - 03 Feb 2001 (China)
You can alleviate the problem, while providing several formats:
// Here we try to support 4 formats (note different delimeters)
string[] formats = new string[] {
"s", // try ISO first
"dd'.'MM'.'yyyy HH':'mm':'ss", // if failed try Russian
"MM'/'dd'/'yyyy HH':'mm':'ss", // on error have a look at USA
"yyyy'-'MM'-'dd HH':'mm':'ss", // the last hope is Chinese
};
bool isValid = DateTime.TryParse(
source,
formats,
CultureInfo.InvariantCulture,
DateTimeStyles.AssumeLocal,
out var date);

string to dateTime convention changes the format of the string

My code is like this
DateTime dt = new DateTime();
dt= DateTime.ParseExact("14/09/2017", "dd/MM/yyyy", CultureInfo.InvariantCulture);
I am expecting dt to have a format of dd/MM/yyyy but the output I am getting is in MM/dd/yyyy format.
This is the correct out put I am getting 9/14/2017 12:00:00 AM.
Can anyone please point out what I am doing wrong here?

if you expect the format "dd/MM/yyyy" you need to specify it when displaying the DateTime. To do so you can use this overload of the ToString method:
dt.ToString("dd/MM/yyyy");
A DateTime on it's own has no format. Only the string representation of it has one.
EDIT:
Important remark by Tim Schmelter:
/ is a custom format specifier which replaces all occurences with the local date-separator. You either have to esacape them by embedding them within ' or use CultureInfo.InvariantCulture as second parameter. Read this post
That means either use this:
string str_rep = dt.ToString("dd'/'MM'/'yyyy");
or:
string str_rep = dt.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);

Your dt is a DateTime, not a string. Format concept only applies when you get their textual (aka string) representation. What you saw is probably what debbuger/ide shows you as a textual representation.
If you get a specific format of your dt, then you can use .ToString() method with dd/MM/yyyy format and a proper culture like InvariantCulture.
string myFormat = dt.ToString("dd/MM/yyyy", CultureInfo.InvariantCulture);
For beginners, it is really important to understand the difference between what is a DateTime and what is their string representation.

If DateTime.ToString() is resulting in an unexpected format, the likely case is that the current culture isn't being set. By default, the date format used is taken from the host machine. However, you can either specify it directly by setting the thread's CurrentCulture for the culture code you need, or you can set it in your application's configuration file. E.g., a web application's web.config can have a globalization section, like so;
<globalization culture="en-GB" uiCulture="en-GB" />
Alternatively, as already specified, you can set the format explicitly via a custom format string .ToString("dd/MM/yyyy").

DateTime.TryParse issue with dates consisting of a.m instead of am

I have the following date in string format "2017-04-05 05:00:00 a.m" . Now I am trying to convert that to datetime format with the following code:
var dateTime="2017-04-05 05:00:00 a.m";
DateTime value = DateTime.MinValue;
DateTime.TryParse(dateTime, out value );
But I am alwayws getting dt as {1/1/0001 12:00:00 AM} , Can you please tell me why ? and how can I convert that string to date.

You could try creating a custom DateTimeFormatInfo with your custom am/pm designators:
var formatInfo = (DateTimeFormatInfo) CultureInfo.InvariantCulture.DateTimeFormat.Clone();
formatInfo.AMDesignator = "a.m";
formatInfo.PMDesignator = "p.m";
var value = DateTime.Parse("2017-04-05 05:00:00 a.m", formatInfo);
This also works for afternoon times:
var value = DateTime.Parse("2017-04-05 03:00:00 p.m", formatInfo);

The DateTime string you have is not parsed and you are getting the default value. One of the reason is the a.m in your date string. It also depends on Current thread Culture settings as well. You can use TryParseExact to give the format you have in DateTime string also with CulureInfo.
DateTime.TryParseExact(dateTime, "yyyy-MM-dd hh:mm:ss 'a.m'", CultureInfo.InvariantCulture,DateTimeStyles.None, out value);
Note you have a.m instead of am which has to be escaped like I did with 'a.m' in above example.
You can have p.m as well and above wont work for that. You can replace dot with empty string to make a.m to am and p.m to pm to use Custom Date and Time Format Strings tt for am / pm. I assume there would be only one dot between am or pm.
string dateTime = "2017-04-05 05:00:00 a.m";
dateTime = dateTime.Replace(".", "");
DateTime value = DateTime.MinValue;
DateTime.TryParseExact(dateTime, "yyyy-MM-dd hh:mm:ss tt", CultureInfo.InvariantCulture,DateTimeStyles.None, out value);
Read more about impact of Thread.CurrentCulture
The CultureInfo object that is returned by this property, together
with its associated objects, determine the default format for dates,
times, numbers, currency values, the sorting order of text, casing
conventions, and string comparisons. See the CultureInfo class to
learn about culture names and identifiers, the differences between
invariant, neutral, and specific cultures, and the way culture
information affects threads and application domains. See the
CultureInfo.CurrentCulture property to learn how a thread's default
culture is determined, and how users set culture information for their
computers.

The . in a.m is causing the problem. Assuming that you have both a.m and p.m to deal with, try stripping the . characters before you try to parse the DateTime value.
var stringToParse = "2017-04-05 05:00:00 a.m";
DateTime parsedValue;
DateTime.TryParse(stringToParse.Replace(".", string.Empty), out parsedValue);
This will not work if a . character is used elsewhere in the string, for any other reason. Fractional seconds for example. If that is the case, you'd be better off using Joe's answer instead.

Convert string to date time and format to specific format in string

the string is 20131024174621 which is year =2013, month=10, date=24, hours=17, minutes=46, seconds=21
What I am trying to do is to convert and format it into 2013-10-24 17:46:21.
I have tried my luck as the code below however it return such error :
String was not recognized as a valid DateTime.
String timestamp = "20131024174621";
String converted = DateTime.Parse(timestamp).ToString("yyyy-MM-dd HH:mm:ss");
What should be the way of doing it right?

You have to use ParseExact.
void Main()
{
String timestamp = "20131024174621";
var date = DateTime.ParseExact(timestamp, "yyyyMMddHHmmss", CultureInfo.InvariantCulture);
Console.WriteLine (date.ToString("yyyy-MM-dd HH:mm:ss"));
}
Output:
2013-10-24 17:46:21

DateTime.ParseExact( timestamp, "yyyyMMddHHmmss", CultureInfo.InvariantCulture ).ToString( "yyyy-MM-dd HH:mm:ss" );

Since other two answer is correct, I want to point the root of your problem.
DateTime.Parse method uses Standard Date and Time Format Strings. From How Standard Format Strings Work
In a formatting operation, a standard format string is simply an alias
for a custom format string. The advantage of using an alias to refer
to a custom format string is that, although the alias remains
invariant, the custom format string itself can vary. This is important
because the string representations of date and time values typically
vary by culture. For example, the "d" standard format string indicates
that a date and time value is to be displayed using a short date
pattern. For the invariant culture, this pattern is "MM/dd/yyyy". For
the fr-FR culture, it is "dd/MM/yyyy". For the ja-JP culture, it is
"yyyy/MM/dd"
In 20131024174621 string, you need yyyyMMddHHmmss format for your current culture. Looks like your culture doesn't have this format and that's why you get this error.
For this kind of non-standart format string, you can use custom date format.
Any string that is not a standard date and time format string is
interpreted as a custom date and time format string.
As I wrote in third paragraph, this kind of date formats is based on culture. When you have this kind of custom date strings, in most case using DateTime.ParseExact Method (String, String, IFormatProvider) with specific culture is the best choice.