A family of Microsoft relational database management systems designed for ease of use.
Since it looks like your buttons are in the header or on the main form, I would just use the double-click event of the StartTime or StopTime to set the value to either Time() or Now() depending on if you want the time to include the date portion. The code would be something like:
Private Sub StartTime_DblClick(Cancel As Integer)
Me.StartTime = Time()
End Sub
Replace the command buttons with a label with the caption "Double-Click to enter current time".