code: def time_period(self):
          
          if self.args.time_period is None:
              if self.args.files or is_pipe(STDIN_FILENO) or is_redirected(STDIN_FILENO):
                  time_period = (None, None)
              else:
                  diff = 86400  # 24h = 86400 seconds
                  time_period = get_datetime_interval(int(time.time()), diff, 3600)
          else:
              time_period = self.args.time_period
  
          logger.debug('time period to be processed: %r', time_period)
          return time_period
docs: Time period that is determined from the arguments --date and --last. It's a 2-tuple with
          (<start datetime>, <end_datetime>) items. An item is `None` if there isn't a limit.