code: def get_last_update_time(self):
          '''
          Gets the time at which each ledger was updated.
          Can be called at any time to get this information.
          :return: an ordered dict of outdated ledgers sorted by last update time (from old to new)
          and then by ledger ID (in case of equal update time)
          '''
          last_updated = {ledger_id: freshness_state.last_updated
                          for ledger_id, freshness_state in self._ledger_freshness.items()}
          return OrderedDict(
              sorted(
                  last_updated.items(),
                  key=lambda item: (item[1], item[0])
              )
          )