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C# parse DateTime String to time only

I am new to C# and I have a string like "2021-06-14 19:27:14:979". Now I want to have only the time "19:27:14:979". So do I parse the string to a specific DateTime format and then convert it back to a string or would you parse or cut the string itself?
It is important that I keep the 24h format. I don't want AM or PM.
I haven't found any solution yet. I tried to convert it to DateTime like:
var Time1 = DateTime.ParseExact(time, "yyyy-MM-dd HH:mm:ss:fff");
var Time2 = Time1.ToString("hh:mm:ss:fff");
But then I lost the 24h format.

Your code is almost working, but ParseExact needs two additional arguments and ToString needs upper-case HH for 24h format:
var Time1 = DateTime.ParseExact("2021-06-14 19:27:14:979", "yyyy-MM-dd HH:mm:ss:fff", null, DateTimeStyles.None);
var Time2 = Time1.ToString("HH:mm:ss:fff");
Read: https://learn.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings#uppercase-hour-h-format-specifier
Instead of passing null as format provider(means current culture) you might want to pass a specifc CultureInfo, for example CultureInfo.CreateSpecificCulture("en-US").

You can just split it at the blank and take the last part like this
var timestamp = "2021-06-14 19:27:14:979";
var timePart = timestamp.Split(' ')[1];
in your case that seems easier than parsing into a DateTime and back into a string.

Converting a string into a 24hr datetime format

I have string data that comes in the following sequence:
"4:32", "1:08"
I want to convert this to 24hr time
where "4:32" becomes 16:32

Parse that to a TimeSpan, then add 12 hours:
var offset = TimeSpan.FromHours(12);
var time = TimeSpan.Parse("4:32").Add(offset);

Parse the input string to a TimeSpan, add 12 hours, then format the TimeSpan with the desired string format:
string input = "4:32";
string output = TimeSpan.Parse(input).Add(TimeSpan.FromHours(12)).ToString("hh\\:mm");
// output: "16:32"

As per your comment, once you know if the hour is AM/PM, you could parse the value with it's suffix and then use the HH custom format specifier:
DateTime d = DateTime.Parse("4:32 PM");
Console.WriteLine(d.ToString("HH:mm"));
to convert it to 24h format.
https://learn.microsoft.com/en-us/dotnet/standard/base-types/custom-date-and-time-format-strings#HH_Specifier

In the simple case your question suggests, where you know beforehand that the string is 12-hour in the format h:mm and it refers to PM, never AM, then you can split the string, parse the hour, add 12, and reassemble it.
var inputString = "4:32";
var splits = inputString.Split(':');
var hourString = splits[0];
var minuteString = splits[1];
var hour = int.Parse(hourString);
hour = hour + 12;
var outputString = $"{hour}:{minuteString}";
If you're doing anything more complicated with dates or times, you probably want to use DateTime or similar classes.

Not getting correct date from DateTime in c#

I need only date in the yyyy-MM-dd format, but I'm getting (20/03/2018 0:00:00) date in wrong format.
var d = Convert.ToDateTime("2018-03-20T00:00:00.000",CultureInfo.InvariantCulture).ToString("yyyy-MM-dd");
var finaldate = DateTime.TryParseExact(d, "yyyy-MM-dd", null);
Output i am getting --20/03/2018 0:00:00
expected -- 2018-03-20

I will try to explain what the others meant when they wrote "DateTime has no format".
DateTime is a C# type that has properties for year, month, day, etc.
If you want to print a DateTime, you first have to convert it to a string. During this conversion, you can define the output format.
Also, if you parse a string into a DateTime, you can define the expected input format.
This is what the "Standard Date and Time Format Strings" / "Custom Date and Time Format Strings" are for.
An example:
string d = Convert.ToDateTime("2018-03-20T00:00:00.000",CultureInfo.InvariantCulture).ToString("yyyy-MM-dd");
DateTime finaldate = DateTime.TryParseExact(d, "yyyy-MM-dd", null); // not a string!
int year = finadate.Year; // year == 2018 (a number!)
int month = finaldate.Month; // month == 3 (a number again!)
string isoFormat = finaldate.ToString("yyyy-MM-dd"); // isoFormat == "2018-03-20"
string usFormat = finaldate.ToString("MM/dd/yyyy"); // usFormat == "03/20/2018"
// and so on...
Note that if you just call ToString() without specifying any format, the result will depend on the culture of the current thread (probably "en-Us" judging from the output you have shown). See DateTime.ToString Method.

DateTime always returns DateTime object with the time part.
To get expected output, you have to return string eg. DateTime.Now.ToString("dd-MM-yyyy")

I need only date value part and time value part using ASP.NET C#

I have two parameters one for date and another for time, and i need date value part and time values part.
My two parameters are below.
// For Date parameter
DateTime dt = DateTime.ParseExact("01-jan-1999", "dd-MMM-yyyy", CultureInfo.InvariantCulture);
bo.Dateused5 = dt;
// For Time parameter
string Fromtiming = ddl_FromHours.SelectedItem.ToString() + ":" + ddl_FromMinutes.SelectedItem.ToString();
DateTime InterviewTime = Convert.ToDateTime(Fromtiming);//StartTime
bo.Dateused4 = InterviewTime;//InterviewTime
so i need to send mail to the candidate to only date part, should not contain time and time part, should not contain date.

are you looking for this:
DateTime dt = DateTime.ParseExact("01-jan-1999", "dd-MMM-yyyy", CultureInfo.InvariantCulture);
string mailDate = dt.ToString("dd-MMM-yyyy");// will give 01-jan-1999
string date = dt.ToString("dd-MM-yyyy"); // will give 01-01-1999
You can also try using String.Format()
string mailDate = String.Format("{0:dd-MM-yyyy}", dt); // will give 01-01-1999

You can use ToShortDateString():
DateTime dt = DateTime.ParseExact("01-jan-1999", "dd-MMM-yyyy", CultureInfo.InvariantCulture);
var date = dt.ToShortDateString();
Note that it uses date format attached to the current thread's culture info.

You would need to use strings rather than dates, so change the type of your variables to string so that
bo.Dateused5 = dt.ToString("dd-MMM-yyyy")
would set Dateused5 to a string of the date component, then
bo.Dateused4 = InterviewTime.ToString("HH:MM");
would set Dateused4 to the time component.

Couldn't test your code but I am very sure there are Functions "DateValue" and "TimeValue" you can make use of.
Something like,
Format(DateValue(any datetime), "dd-MM-yyyy")
gives you Only Date in the specified format. Similar way for TimeValue

how to convert 24-hour format TimeSpan to 12-hour format TimeSpan?

I have TimeSpan data represented as 24-hour format, such as 14:00:00, I wanna convert it to 12-hour format, 2:00 PM, I googled and found something related in stackoverflow and msdn, but didn't solve this problem, can anyone help me? Thanks in advance.
Update
Seems that it's possible to convert 24-hour format TimeSpan to String, but impossible to convert the string to 12-hour format TimeSpan :(
But I still got SO MANY good answers, thanks!

(Summing up my scattered comments in a single answer.)
First you need to understand that TimeSpan represents a time interval. This time interval is internally represented as a count of ticks an not the string 14:00:00 nor the string 2:00 PM. Only when you convert the TimeSpan to a string does it make sense to talk about the two different string representations. Switching from one representation to another does not alter or convert the tick count stored in the TimeSpan.
Writing time as 2:00 PM instead of 14:00:00 is about date/time formatting and culture. This is all handled by the DateTime class.
However, even though TimeSpan represents a time interval it is quite suitable for representing the time of day (DateTime.TimeOfDay returns a TimeSpan). So it is not unreasonable to use it for that purpose.
To perform the formatting described you need to either rely on the formatting logic of DateTime or simply create your own formatting code.
Using DateTime:
var dateTime = new DateTime(timeSpan.Ticks); // Date part is 01-01-0001
var formattedTime = dateTime.ToString("h:mm tt", CultureInfo.InvariantCulture);
The format specifiers using in ToString are documented on the Custom Date and Time Format Strings page on MSDN. It is important to specify a CultureInfo that uses the desired AM/PM designator. Otherwise the tt format specifier may be replaced by the empty string.
Using custom formatting:
var hours = timeSpan.Hours;
var minutes = timeSpan.Minutes;
var amPmDesignator = "AM";
if (hours == 0)
hours = 12;
else if (hours == 12)
amPmDesignator = "PM";
else if (hours > 12) {
hours -= 12;
amPmDesignator = "PM";
}
var formattedTime =
String.Format("{0}:{1:00} {2}", hours, minutes, amPmDesignator);
Admittedly this solution is quite a bit more complex than the first method.

TimeSpan represents a time interval not a time of day. The DateTime structure is more likely what you're looking for.

You need to convert the TimeSpan to a DateTime object first, then use whatever DateTime format you need:
var t = DateTime.Now.TimeOfDay;
Console.WriteLine(new DateTime(t.Ticks).ToString("hh:mm:ss tt"));
ToShortTimeString() would also work, but it's regional-settings dependent so it would not display correctly (or correctly, depending on how you see it) on non-US systems.

TimeSpan represents a time interval (a difference between times),
not a date or a time, so it makes little sense to define it in 24 or 12h format. I assume that you actually want a DateTime.
For example 2 PM of today:
TimeSpan ts = TimeSpan.FromHours(14);
DateTime dt = DateTime.Today.Add(ts);
Then you can format that date as you want:
String formatted = String.Format("{0:d/M/yyyy hh:mm:ss}", dt); // "12.4.1012 02:00:00" - german (de-DE)
http://msdn.microsoft.com/en-us/library/az4se3k1%28v=vs.100%29.aspx

Try This Code:
int timezone = 0;
This string gives 12-hours format
string time = DateTime.Now.AddHours(-timezone).ToString("hh:mm:ss tt");
This string gives 24-hours format
string time = DateTime.Now.AddHours(-timezone).ToString("HH:mm:ss tt");

Assuming you are staying in a 24 hour range, you can achieve what you want by subtracting the negative TimeSpan from Today's DateTime (or any date for that matter), then strip the date portion:
DateTime dt = DateTime.Today;
dt.Subtract(-TimeSpan.FromHours(14)).ToShortTimeString();
Yields:
2:00 PM

String formatted = yourDateTimeValue.ToString("hh:mm:ss tt");

It is very simple,
Let's suppose we have an object ts of TimesSpan :
TimeSpan ts = new TimeSpan();
and suppose it contains some value like 14:00:00
Now first convert this into a string and then in DateTime
as following:
TimeSpan ts = new TimeSpan(); // this is object of TimeSpan and Suppose it contains
// value 14:00:00
string tIme = ts.ToString(); // here we convert ts into String and Store in Temprary
// String variable.
DateTime TheTime = new DateTime(); // Creating the object of DateTime;
TheTime = Convert.ToDateTime(tIme); // now converting our temporary string into DateTime;
Console.WriteLine(TheTime.ToString(hh:mm:ss tt));
this will show the Result as: 02:00:00 PM

Normal Datetime can be converted in either 24 or 12 hours format.
For 24 hours format - MM/dd/yyyy HH:mm:ss tt
For 12 hours format - MM/dd/yyyy hh:mm:ss tt
There is a difference of captial and small H.
dateTimeValue.ToString(format, CultureInfo.InvariantCulture);