timer-scheduledTimer.swift

var startNumber = 240
var timer = Timer()
func runTime() {
        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: (#selector(ViewController.tTimer)), userInfo: nil, repeats: true)
    }

@objc func tTimer() {
    if startNumber > 0 {
        startNumber -= 1
        numberLabel.text = String(startNumber)
    }else{
        timer.invalidate()
    }
}