Return business hours in a day by seconds.

def _get_business_hours_by_sec(self):
        """
        Return business hours in a day by seconds.
        """
        if self._get_daytime_flag:
            # create dummy datetime to calculate businesshours in a day
            dtstart = datetime(2014, 4, 1, self.start.hour, self.start.minute)
            until = datetime(2014, 4, 1, self.end.hour, self.end.minute)
            return (until - dtstart).total_seconds()
        else:
            dtstart = datetime(2014, 4, 1, self.start.hour, self.start.minute)
            until = datetime(2014, 4, 2, self.end.hour, self.end.minute)
            return (until - dtstart).total_seconds()