code: def txn2epoch(self, txn: dict) -> int:
          
  
          rv = None
          if self == Protocol.V_13:
              rv = txn['result']['txnTime']
          else:
              rv = txn['result']['txnMetadata']['txnTime']
  
          return rv
docs: Given ledger transaction, return its epoch time.
  
          :param txn: transaction as dict
          :return: transaction time