code: def timer_cb(self, timer):
          
          dt_now = datetime.utcnow().replace(tzinfo=pytz.utc)
          self.logger.debug("timer fired. utc time is '%s'" % (str(dt_now)))
  
          for clock in self.clocks.values():
              clock.update_clock(dt_now)
  
          # update clocks approx every second
          timer.start(1.0)
docs: Timer callback.  Update all our clocks.