add a countdown timer before a countdown timer (swift3)

In my code if you press the startButton countdown goes from 60 - 0 . All I want to do is have a countdown from 3 - 0 then countdown from 60 - 0. Think of it mark, set, go then start the countdown timer from 60 seconds to 0.

 import UIKit
class ViewController: UIViewController {

@IBOutlet weak var startButton: UIButton!
@IBOutlet weak var timerLabel: UILabel!

var seconds = 60
var timer = Timer()
var isTimerRunning = false
var resumeTapped = false

@IBAction func startButtonTapped(_ sender: UIButton) {
    if isTimerRunning == false {
        runTimer()
        self.startButton.isEnabled = false
    }
}

func runTimer() {
    timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: (#selector(ViewController.updateTimer)), userInfo: nil, repeats: true)
    isTimerRunning = true

}
@IBAction func resetButtonTapped(_ sender: UIButton) {
    timer.invalidate()
    seconds = 60
    timerLabel.text = timeString(time: TimeInterval(seconds))
    isTimerRunning = false

}

//MARK: - Public Method
func updateTimer(){
    if seconds < 1 {
        timer.invalidate()
        //Send alert to indicate time's up.
    } else {
        seconds -= 1
        timerLabel.text = timeString(time: TimeInterval(seconds))
    }
}

func timeString(time:TimeInterval) -> String {
    let hours = Int(time) / 3600
    let minutes = Int(time) / 60 % 60
    let seconds = Int(time) % 60
    return String(format:"%02i:%02i:%02i", hours, minutes, seconds)
    }}