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Change DateTime Format {"MM/dd/yyyy"} to {"dd/MM/yyyy"} and time should remain same in Unity

I want to change DateTime now to the Format {"MM/dd/yyyy"} using this code.
string.Format("{0:MM:dd:yyyy}", DateTime.Now)
and saving it.
after getting saved string I get DateTime in format {"MM/dd/yyyy"} . Now I want to convert it in another format so I can Parse to DateTime. when I try to parse MM/dd/yyyy to DateTime got an error
"FormatException: String was not recognized as a valid DateTime."
Thanks in Advance.

You can rather use DateTime.ParseExact which allows you to specify the exact date format you are expeting the input to have.
For example
var now = DateTime.Now;
Debug.Log(now.ToString("dd.MM.yyyy"));
var example1 = now.ToString("MM/dd/yyyy");
Debug.Log(example1);
var readTime1 = DateTime.ParseExact(example1, "MM/dd/yyyy", CultureInfo.InvariantCulture);
Debug.Log(readTime1.ToString("dd.MM.yyyy"));
var example2 = now.ToString("dd/MM/yyyy");
Debug.Log(example2);
var readTime2 = DateTime.ParseExact(example2, "dd/MM/yyyy", CultureInfo.InvariantCulture);
Debug.Log(readTime2.ToString("dd.MM.yyyy"));
See Fiddle

The format is only relevant for display
If you save it in a C# DateTime variable, there is no "format" when saving it, this DateTime is a struct data type which is universal and not bound to any specific format
If you want to use a specific format for parsing, you can use:
// Parse date and time with custom specifier.
CultureInfo provider = CultureInfo.InvariantCulture;
dateString = "Sun 15 Jun 2008 8:30 AM -06:00";
format = "ddd dd MMM yyyy h:mm tt zzz";
DateTime myDate = DateTime.ParseExact(dateString, format, provider);
You can use CultureInfo to optimize your format for you needs
If there is a need to save it as "MM/dd/yyyy", your should save it as string
best regards

DateTime.ParseExact not working in C#, Date format Conversion not working

Parse Time not working as I want to convert "13-06-2019 00:00:00"(dd-MM-yyyy HH:mm:ss) to "06-13-2019 00:00:00"(MM-dd-yyyy HH:mm:ss)
tried with Convert.toDateTime() and DateTime.ParseExact()
IFormatProvider culture = new CultureInfo("en-US");
var a = DateTime.ParseExact(a, "MM-dd-yyyy hh:mm:ss", CultureInfo.InvariantCulture);
var b = DateTime.ParseExact(a, "yyyy-MM-dd HH:mm:ss", null);
var c = DateTime.ParseExact(a, "yyyy-MM-dd HH:mm:ss", culture);
Nothing working in it

DateTime structure uses Gregorian calendar under the hood and there is no 13th month in that calendar.
So, parsing 13 with MM specifier is wrong. I strongly suspect that you try to use dd-MM-yyyy HH:mm:ss format instead.
string a = "13-06-2019 00:00:00";
DateTime b = DateTime.ParseExact(a, "dd-MM-yyyy HH:mm:ss", CultureInfo.InvariantCulture);
Here a demonstration
Your second and third examples also don't work since their formats are completely different than your string. When you parse your string with ParseExact method, your strings and your format should match exactly.
Also I want to mention that, both hh and HH specifiers would work in my code example. But as a general format consideration, using dd-MM-yyyy HH:mm:ss format is much more common and reliable than the other option.

The format parameter of DateTime.ParseExact(date,format,culture) is the source format of the date string to be converted and the return value is type date which you can convert back to string as per the desired format.
var a = "13-06-2019 00:00:00";
IFormatProvider culture = new CultureInfo("en-US");
DateTime b = DateTime.ParseExact(a, "dd-MM-yyyy hh:mm:ss", CultureInfo.InvariantCulture);
Console.WriteLine($"{b:MM-dd-yyyy HH:mm:ss}");

How to find exact format of a date string?

I need to know exact date format that will perse the string 16-Aug-78 12:00:00 AM. I have tried various string like "ss-MMM-yy hh:mm:ss". Is there any way for finding it to converting to any general format. I am using CultureInfo.InvariantCulture class.

Your string format is wrong. It has to match your string format exactly. You can use dd-MMM-yy hh:mm:ss tt format instead.
Here an example in LINQPad.
string s = "16-Aug-78 12:00:00 AM";
var date = DateTime.ParseExact(s, "dd-MMM-yy hh:mm:ss tt",
CultureInfo.InvariantCulture);
date.Dump();
Custom Date and Time Format Strings
Or, since dd-MMM-yy hh:mm:ss tt is a standart date and time format for InvariantCulture, you can directly DateTime.Parse method like;
string s = "16-Aug-78 12:00:00 AM";
var date = DateTime.Parse(s, CultureInfo.InvariantCulture);
date.Dump();
Here a demonstration.
Is there any way for finding it to converting to any general format?
There is no way to get format of a string except you create your own formatting. Only you can know what is your string format exactly, computer can't.
For example; 01/02/2014 can be 1 February 2014 or 2 January 2014 depends on which custom format you can parse it.

Try as below
var dstring = "16-Aug-78 12:00:00 AM";
DateTime result;
var matchingCulture = CultureInfo.GetCultures(CultureTypes.AllCultures).FirstOrDefault(ci => DateTime.TryParse(dstring, ci, DateTimeStyles.None, out result))

You have wrong format string, you are using ss for day it should be dd. This article Custom Date and Time Format Strings explains what you need for custom format.
Use
"dd-MMM-yy hh:mm:ss tt"
Instead of
"ss-MMM-yy hh:mm:ss"
You can use DateTime.ParseExact to parse the string.
DateTime dt = DateTime.ParseExact("16-Aug-78 12:00:00 AM", "dd-MMM-yy hh:mm:ss tt", CultureInfo.InvariantCulture, DateTimeStyles.None);

You can try with DateTime.TryParseExact():
string strDate = "16-Aug-78 12:00:00 AM";
DateTime datDate;
if(DateTime.TryParseExact(strDate , new string[] {"dd-MMM-yy hh:mm:ss tt" },
System.Globalization.CultureInfo.InvariantCulture,
System.Globalization.DateTimeStyles.None, out datDate))
{
Console.WriteLine(datDate);
}
else
{
Console.WriteLine("Error in datetime format");
}

Getting an error while converting string to DateTime

I am trying to convert a string value into DateTime. It gives me an error as, specified string is not in correct format.
Here is the code,
DateTime myDate = DateTime.ParseExact("07-09-2013 01:14:14:1414", "yyyy-MM-dd HH:mm:ss", System.Globalization.CultureInfo.InvariantCulture);
string strDate = "07/09/2013 01:04:02:4";
Convert.ToDateTime(strDate);
DateTime dt = DateTime.Parse(strDate);
Please help in converting the same.
Thanks

Your format seems to be incorrect. Should be:
"dd-MM-yyyy HH:mm:ss:ffff"
Update. If number of digits representing fractions of a second varies, than the best bet is
"dd-MM-yyyy HH:mm:ss:FFFFFFF"
Refer to MSDN for other options for custom time and date formats.

Try in your page_load event:
Thread.CurrentThread.CurrentUICulture = New System.Globalization.CultureInfo("tr-TR")
Thread.CurrentThread.CurrentCulture = New System.Globalization.CultureInfo("tr-TR")

First, you mixed you years place
07-09-2013 is dd-MM-yyyy format
second, you need a :ffff after seconds
So the final line should be
DateTime myDate = DateTime.ParseExact("2013-07-09 01:14:14:1414", "yyyy-MM-dd HH:mm:ss:ffff", System.Globalization.CultureInfo.InvariantCulture);

Your format isn't correct:
"07-09-2013 01:14:14:1414"
"yyyy-MM-dd HH:mm:ss"
Atleast your date is the other way around, and the milliseconds is not specified.
Correct you format according to this: http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx
For the downvoter:
The correct format is specified by Andrei: "dd-MM-yyyy HH:mm:ss:ffff"

First of all, you should change your date format to dd-MM-yyyy because it fits with your date format.
Second of all, for miliseconds part, you can use . instead of :
DateTime myDate = DateTime.ParseExact("07-09-2013 01:14:14.1414", "dd-MM-yyyy HH:mm:ss.ffff", System.Globalization.CultureInfo.InvariantCulture);
string strDate = "07/09/2013 01:04:02.4";
Convert.ToDateTime(strDate);
DateTime dt = DateTime.Parse(strDate);
Here a DEMO.
For more information, check Custom Date and Time Format Strings

Display datetime into MM/dd/yyyy HH:mm format c#

In database datetime is being stored in MM-dd-yyyy HH:mm:ss fromat.
However, I want to display datetime in "MM/dd/yyyy HH:mm" format.
I tried it by using String.Format().
txtCampaignStartDate.Text = String.Format("{0:MM/dd/yyyy
HH:mm}",appCampaignModel.CampaignStartDateTime);
Here appCampaignModel.CampaignStartDateTime is DateTime object having value in "MM-dd-yyyy HH:mm" format.
I want to display in "MM/dd/yyyy HH:mm" format.
Can anyone help me for this?

The slashes in this format MM/dd/yyyy HH:mm mean: "replace me with the actual separator of the current culture". You have to use CultureInfo.InvariantCulture explicitely:
txtCampaignStartDate.Text = appCampaignModel.CampaignStartDateTime.ToString("MM/dd/yyyy HH:mm", CultureInfo.InvariantCulture);
The "/" Custom Format Specifier
In database datetime is being stored in MM-dd-yyyy HH:mm:ss fromat.
Don't store datetimes with a format which means that you store them as (n)varchar. Use datetime instead.

txtCampaignStartDate.Text = appCampaignModel.CampaignStartDateTime
.ToString().Replace("-","/");
or
String.Format("{0:MM/dd/yyyy HH:mm}", dt);
Check : String Format for DateTime [C#]
or
String date = dt.ToString("MM/dd/yyyy HH:mm", DateTimeFormatInfo.InvariantInfo);
DateTime.ToString Method (String, IFormatProvider)

Why not just a simple replace?
txtCampaignStartDate.Text = BadString.Replace("-","/");

try using an added culture info:
CultureInfo ci = new CultureInfo("en-US");
txtCampaignStartDate.Text =
appCampaignModel.CampaignStartDateTime.ToString("MM/dd/yyyy HH:mm", ci);
p.s. the culture info used is an example.

To display your date in format you specified:
txtCampaignStartDate.Text = appCampaignModel.CampaignStartDateTime.ToString("g",DateTimeFormatInfo.InvariantInfo)
And for more date time formats you can go through this link.

Since you already have a DateTime object, just ToString it how you want:
appCampaignModel.CampaignStartDateTime.ToString("MM/dd/yyyy HH:mm");