code: def add_answer_at_time(self, record, now):
          
          if record is not None:
              if now == 0 or not record.is_expired(now):
                  self.answers.append((record, now))
                  if record.rrsig is not None:
                      self.answers.append((record.rrsig, now))
docs: Adds an answer if if does not expire by a certain time