Using a timer for a game in swift

I am using a timer for a game in Swift. It controls the speed of asteroids falling. I would like the speed of the asteroids to fall more quickly after the score has reached a certain level, however, the speed remains the same. I suspect this is because the repeat value is set to true and it is stuck in a loop of sorts.

    if score <= 10 {
    Timer.scheduledTimer(timeInterval: TimeInterval(Helper().randomBetweenTwoNumbers(firstNumber: 0.8, secondNumber: 5)), target: self, selector: #selector (GameScene.leftTraffic), userInfo: nil, repeats: true)
    Timer.scheduledTimer(timeInterval: TimeInterval(Helper().randomBetweenTwoNumbers(firstNumber: 0.8, secondNumber: 5)), target: self, selector: #selector (GameScene.rightTraffic), userInfo: nil, repeats: true)
    }else {
        Timer.scheduledTimer(timeInterval: TimeInterval(Helper().randomBetweenTwoNumbers(firstNumber: 0.8, secondNumber: 1)), target: self, selector: #selector (GameScene.leftTraffic), userInfo: nil, repeats: true)
        Timer.scheduledTimer(timeInterval: TimeInterval(Helper().randomBetweenTwoNumbers(firstNumber: 0.8, secondNumber: 1)), target: self, selector: #selector (GameScene.rightTraffic), userInfo: nil, repeats: true)
    }

Any help would be greatly appreciated!

Thanks!!