code: func NewTimer(fn Func, interval time.Duration, counter int) *Timer {
  	id := atomic.AddInt64(&Manager.incrementID, 1)
  	t := &Timer{
  		ID:       id,
  		fn:       fn,
  		createAt: time.Now().UnixNano(),
  		interval: interval,
  		elapse:   int64(interval), // first execution will be after interval
  		counter:  counter,
  	}
  
  	// add to manager
  	Manager.ChCreatedTimer <- t
  	return t
  }
docs: // NewTimer creates a cron job