Sets the length of time between the start and end times.  The inputed
        number should represent the number of minutes in between them, and
        will be automatically rounded to the nearest 15 minutes.
        
        :param      length | <int>

def setLength( self, length ):
        """
        Sets the length of time between the start and end times.  The inputed
        number should represent the number of minutes in between them, and
        will be automatically rounded to the nearest 15 minutes.
        
        :param      length | <int>
        """
        self._timeEnd = self._timeStart.addSecs((length - length % 15) * 60)
        self.markForRebuild()