code: def format_time_trigger_string(timer_instance):
      
      if isinstance(timer_instance, RepeatTimer):
          return TRIGGER_PREAMBLE_EVERY + str(timer_instance.interval_new)
      elif isinstance(timer_instance, EventClock):
          timestamps = [repr(x) for x in timer_instance.timestamps]
          return TRIGGER_PREAMBLE_AT + ','.join(timestamps)
      else:
          raise ValueError('Unknown timer instance type {0}'.format(timer_instance.__class__.__name__))
docs: :param timer_instance: either instance of RepeatTimer or EventClock
      :return: human-readable and editable string in one of two formats:
       - 'at Day_of_Week-HH:MM, ..., Day_of_Week-HH:MM'
       - 'every NNN'