If Me.EndTime < Me.StartTime Then
Me.YourTextBox = [URL="http://www.techonthenet.com/access/functions/date/datediff.php"]DateDiff[/URL]("n", Me.StartTime, "23:59") + 1 + DateDiff("n", "00:00", Me.EndTime)
Else
Me.YourTextBox = DateDiff("n", Me.StartTime, Me.EndTime)
End If