code: func (s *Signature) SleepString() string {
  	if s.SleepMax == 0 {
  		return ""
  	}
  	if s.SleepMin != s.SleepMax {
  		return fmt.Sprintf("%d~%d minutes", s.SleepMin, s.SleepMax)
  	}
  	return fmt.Sprintf("%d minutes", s.SleepMax)
  }
docs: // SleepString returns a string "N-M minutes" if the goroutine(s) slept for a
  // long time.
  //
  // Returns an empty string otherwise.