maybe u wouldnt need a API call for that. maybe something like this:

Dim sTime as String, sDate as String

Private Sub cmdLock_Click()
sTime = Time
sDate = Date
tmrReset.Interval = 1000
End Sub

Private Sub tmrReset_Timer()
Time = sTime
Date = sDate
End Sub

Private Sub cmdUnlock_Click()
tmrReset.Interval = 0
End Sub

This way, even if the clock and/or date is changed by another program, then it will be reset to the time when the Lock button was pressed!!!
and for more protection, just decrease the tmrReset.Interval value!!