Converting datetime to time in C# / ASP.NET

The .NET Framework does not have a native Time data type to represent a time of day. You will have to decide between one of the three following options:

Option 1

Use a DateTime type, and ignore the date portion. Pick a date that's outside of a normal range of values for your application. I typically use 0001-01-01, which is conveniently available as DateTime.MinValue.

If you are parsing a time from a string, the easiest way to do this is with the DateTimeStyles.NoCurrentDateDefault option. Without this option, it would use today's date instead of the min date.

DateTime myTime = DateTime.Parse("12:34", CultureInfo.InvariantCulture,
                                          DateTimeStyles.NoCurrentDateDefault);

// Result:  0001-01-01 12:34:00

Of course, if you prefer to use today's date, you can do that. I just think it confuses the issue because you might be looking to apply this to some other date entirely.

Note that once you have a DateTime value, you can use the .TimeOfDay property to get at just the time portion, represented as a TimeSpan, which leads to option 2...

Option 2

Use a TimeSpan type, but be careful in how you interpret it. Understand that TimeSpan is first and foremost a type for representing an elapsed duration of time, not a time of day. That means it can store more than 24 hours, and it can also store negative values to represent moving backwards in time.

When you use it as a time of day, you might be inclined to think of it as "elapsed time since midnight". This, however, will get you into trouble because there are days where midnight does not exist in the local time zone.

For example, October 20th 2013 in Brazil started at 1:00 AM due to daylight saving time. So a TimeSpan of 8:00 on this day would actually have been only 7 hours elapsed since 1:00, not 8 hours elapsed since midnight.

Even in the United States, for locations that use daylight saving time, this value is misleading. For example, November 3rd 2013 in Los Angeles had a duplicated hour for when DST rolled back. So a TimeSpan of 8:00 on this day would actually had 9 hours elapsed since midnight.

So if you use this option, just be careful to treat it as the representative time value that matches a clock, and not as "time elapsed since midnight".

You can get it directly from a string with the following code:

TimeSpan myTime = TimeSpan.Parse("12:34", CultureInfo.InvariantCulture);

Option 3

Use a library that has a true "time of day" type. You'll find this in Noda Time, which offers a much better API for working with date and time in .NET.

The type that represents a "time of day" is called LocalTime, and you can get one from a string like this:

var pattern = LocalTimePattern.CreateWithInvariantCulture("HH:mm");
LocalTime myTime = pattern.Parse("12:34").Value;

Since it appears from your question that you are working with time and attendance data, I strongly suggest you use Noda Time for all your date and time needs. It will force you to put more thought into what you are doing. In the process, you will avoid the pitfalls that can come about with the built-in date/time types.

If you are storing a Time type in your database (such as SQL server), that gets translated as a TimeSpan in .Net. So if you go with this option, you'll need to convert the LocalTime to a TimeSpan as follows:

TimeSpan ts = new TimeSpan(myTime.TickOfDay);