Time calculating

I found nice sample in this forum, how to calculate the time.

 Dim dtStartTime As New Date(2019,9,29,09,00,00)
  Dim dtNow As New Date (2019,9,29,17,30,00)
  Dim i As Integer = dtNow.TotalSeconds - dtStartTime.TotalSeconds
  Dim dtresult As New Date
  dtresult.TotalSeconds = i
  MsgBox dtresult.sqldatetime.NthField(" ",2)

But the sample shows how to do it with fixed time.
My goals is calculating between two times based from actual time and using two button ‘start’ and ‘stop’

any helps,


the result should not be a date but a dateinterval