Returns :data:`True` when the system clock reads between
        :attr:`start_time` and :attr:`end_time`, and :data:`False` otherwise.
        If :attr:`start_time` is greater than :attr:`end_time` (indicating a
        period that crosses midnight), then this returns :data:`True` when the
        current time is greater than :attr:`start_time` or less than
        :attr:`end_time`.

def value(self):
        """
        Returns :data:`True` when the system clock reads between
        :attr:`start_time` and :attr:`end_time`, and :data:`False` otherwise.
        If :attr:`start_time` is greater than :attr:`end_time` (indicating a
        period that crosses midnight), then this returns :data:`True` when the
        current time is greater than :attr:`start_time` or less than
        :attr:`end_time`.
        """
        now = datetime.utcnow().time() if self.utc else datetime.now().time()
        if self.start_time < self.end_time:
            return self.start_time <= now <= self.end_time
        else:
            return not self.end_time < now < self.start_time