code: def next_run_in(self, utc_now=None):
          
          if utc_now is None:
              utc_now = datetime.utcnow()
  
          if self.is_alive():
              next_run = timedelta(seconds=self.interval_current) + self.activation_dt
              return next_run - utc_now
          else:
              return None
docs: :param utc_now: optional parameter to be used by Unit Tests as a definition of "now"
              :return: timedelta instance presenting amount of time before the trigger is triggered next time
           or None if the RepeatTimer instance is not running