'Enter function into the scheduler.
Arguments:
entry (~kombu.async.timer.Entry): Item to enter.
eta (datetime.datetime): Scheduled time.
priority (int): Unused.'

def enter_at(self, entry, eta=None, priority=0, time=monotonic):

    if (eta is None):
        eta = time()
    if isinstance(eta, datetime):
        try:
            eta = to_timestamp(eta)
        except Exception as exc:
            if (not self.handle_error(exc)):
                raise
            return
    return self._enter(eta, priority, entry)
