Android Question DateTime calculatios

Please, anobody can help me??

What am I doing wrong?

Dim StartTrip AsLong = DateTime.TimeParse("08:00:00")
Dim EndTrip AsLong = DateTime.TimeParse("18:30:00")
Dim MovementTime AsLong = DateTime.TimeParse("7:15:00")

Dim TripDuration AsLong = EndTrip - StartTrip
Dim StopTime AsLong = TripDuration - MovementTime

Log("Duration = " & DateTime.Time(TripDuration))
Log("Movement = " & DateTime.Time(MovementTime))
Log("Stoped = " & DateTime.Time(StopTime))


** Activity (main) Create, isFirst = true **
** Activity (main) Resume **

Duration = 10:30:00
Movement = 07:15:00
Stoped = 04:15:00