Without stoping a timer, start again : will it cause running multiple timers in swift

I have a function like below:

func startTimer() {
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    DispatchQueue.main.async {
        appDelegate.TIMER = Timer.scheduledTimer(withTimeInterval: self.REPEAT_TIME, repeats: true, block: { timer in                
            self.sendData(programID: self.MAIN_THREAD)
            do {
                try ...
            }
            catch let error {
                ...
            }
        })
    }
}

Timer Stop Function:

func stopTimer() {
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    if (appDelegate.TIMER != nil) {
        appDelegate.TIMER?.invalidate()
        appDelegate.TIMER = nil
    }
}

I want to know that

1. is there any chance to start multiple timer instances if I call this function without stopping?

2. And how about this case,(does this stopped only one timer & continue running another timer?)
   Start the timer → Start again → Stop