Sets the start time for this item.  This will automatically push the
        end time to match the length for this item.  So if the item starts
        at 11a and ends on 1p, and the start time is changed to 12p
        the end time will change to 2p.  To affect the length of the 
        item, use either setLength, or setTimeEnd.
        
        :param      timeStart | <QDate>

def setTimeStart( self, timeStart ):
        """
        Sets the start time for this item.  This will automatically push the
        end time to match the length for this item.  So if the item starts
        at 11a and ends on 1p, and the start time is changed to 12p
        the end time will change to 2p.  To affect the length of the 
        item, use either setLength, or setTimeEnd.
        
        :param      timeStart | <QDate>
        """
        timeStart = QTime(timeStart)
        
        length = self.length() # in minutes
        self._timeStart = timeStart
        self._timeEnd   = timeStart.addSecs(length * 60)
        self.markForRebuild()