code: def update_scheduled_time(self, when):
          
          tiger = self.tiger
  
          ts = get_timestamp(when)
          assert ts
  
          pipeline = tiger.connection.pipeline()
          key = tiger._key(SCHEDULED, self.queue)
          tiger.scripts.zadd(key, ts, self.id, mode='xx', client=pipeline)
          pipeline.zscore(key, self.id)
          _, score = pipeline.execute()
          if not score:
              raise TaskNotFound('Task {} not found in queue "{}" in state "{}".'.format(
                  self.id, self.queue, SCHEDULED
              ))
  
          self._ts = ts
docs: Updates a scheduled task's date to the given date. If the task is not
          scheduled, a TaskNotFound exception is raised.