System.TimeSpan

Represents a period of time, for example 2 hours, 15 minutes
Allows you to store a measured interval of time
TimeSpan stored its time interval as the number of ticks equal to that interval

Dim objTimeSpan As System.TimeSpan
objTimeSpan = System.TimeSpan.FromDays(2)

This is measures as a positive or negative number of days, hours, minutes and seconds (as fractions)

Dim objTimeSpan As System.TimeSpan
objTimeSpan = New System.TimeSpan(2,12,0,0) ' 2.5 days
objTimeSpan = New System.TimeSpan(4,12) '4.5 days
objTimeSpan = New System.TimeSpan(2,14,18) '??

TimeSpan.Zero
objTimeSpan = objDateTime1 - objDateTime2

in .NET 4.0 the timespan structure supports custom formatting using the .ToString method ??

Operators Supported

You can add or subtract time durations using the normal operators.