code: func (t *timer) enable(d time.Duration) {
  	t.target = time.Now().Add(d)
  
  	// Check if we need to set the runtime timer.
  	if t.state == timerStateDisabled || t.target.Before(t.runtimeTarget) {
  		t.runtimeTarget = t.target
  		t.timer.Reset(d)
  	}
  
  	t.state = timerStateEnabled
  }
docs: // enable enables the timer, programming the runtime timer if necessary.