Arguments must have "start" and "end" properties which are FrameTimes.

def _getDeltas(self, firstSub, secondSub):
        """Arguments must have "start" and "end" properties which are FrameTimes."""
        startDelta = max(firstSub.start, secondSub.start) - min(firstSub.start, secondSub.start)
        endDelta = max(firstSub.end, secondSub.end) - min(firstSub.end, secondSub.end)
        return (startDelta, endDelta)