A DateTime instance stores both date and time information. The DateTime class can be found in the System namespace.
In order to retrieve the current system time, we can use the static property Now of the DateTime class.

In this Example i have shown, how to calculate the difference between two DateTime objects using C# syntax.

 DateTime startTime;
 DateTime endTime;

            startTime = Convert.ToDateTime("12:12 AM");

            endTime = Convert.ToDateTime("1:12 AM");

            var timeDifference = new TimeSpan(endTime.Ticks - startTime.Ticks);

Response.Write("Time difference in hours is " + timeDifference.Hours);


Link:http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx