code: func (t *timeFlag) UnmarshalFlag(value string) error {
  	valueInt, err := strconv.Atoi(value)
  	if err == nil {
  		// We received a number without a unit, assume milliseconds.
  		t.setDuration(time.Duration(valueInt) * time.Millisecond)
  		return nil
  	}
  
  	d, err := time.ParseDuration(value)
  	if err != nil {
  		return err
  	}
  
  	t.setDuration(d)
  	return nil
  }
docs: // UmarshalFlag satisfies the flag interface