Look at DateTime.Add and DateTime.Subtract. You should also look at the TimeSpan class. DateTime.Add takes a TimeSpan parameter and .Subtract takes either a DateTime parameter, which returns a TimeSpan, or a TimeSpan parameter, which returns a DateTime. TimeSpan has Days, Hours, Minutes, and Seconds properties that you can use without having to do the conversions yourself.
-Dell
A computer only does what you actually told it to do - not what you thought you told it to do.