Private Sub Text1_Change()
  On Error Resume Next
 
  Dim Datum1 As Date
  Dim Datum2 As Date
 
  Datum1 = CDate(Text1.Text)
  Datum2 = CDate(Text2.Text)
 
  Text3.Text = CStr(Hour(Datum2 - Datum1) + (Minute(Datum2 - Datum1) / 60))
 
  If Error <> "" Then Text3.Text = ""
End Sub
 
Private Sub Text2_Change()
 
  Call Text1_Change
 
End Sub

Viel Spass,
R@lf