here is an example,
Dim t1 As TimeSpan
Dim dt2 As DateTime = Convert.ToDateTime("01/01/2001 02:00")
Dim dt1 As DateTime = Convert.ToDateTime("01/01/2001 01:30")
t1 = dt2.Subtract(dt1)
Dim duration = t1.Hours.ToString("00") & ":" & t1.Minutes.ToString("00")
Happy Coding!
:)