话不多说，直接上代码！~

定时器

import UIKit

class XT_ZJTimer: NSObject {
    private(set) var _timer: Timer!
    fileprivate weak var _aTarget: AnyObject!
    fileprivate var _aSelector: Selector!
    var fireDate: Date {
        get{
            return _timer.fireDate
        }
        set{
            _timer.fireDate = newValue
        }
    }
    
    class func scheduledTimer(timeInterval ti: TimeInterval, target aTarget: AnyObject, selector aSelector: Selector, userInfo: Any?, repeats yesOrNo: Bool) -> XT_ZJTimer {
        let timer = XT_ZJTimer()
        
        timer._aTarget = aTarget
        timer._aSelector = aSelector
        timer._timer = Timer.scheduledTimer(timeInterval: ti, target: timer, selector: #selector(XT_ZJTimer.zj_timerRun), userInfo: userInfo, repeats: yesOrNo)
        return timer
    }
    
    func fire() {
        _timer.fire()
    }
    
    func invalidate() {
        _timer.invalidate()
    }
    
    @objc func zj_timerRun() {
        //如果崩在这里，说明你没有在使用Timer的VC里面的deinit方法里调用invalidate()方法
        _ = _aTarget.perform(_aSelector)
    }
    
    deinit {
        print("计时器已销毁")
    }
}

需要调用的类封装

import UIKit

class XT_IntimateLoversTimer {
    /// 活动结束秒数
    var secondsToEnd: Int = 0
    var myTimer: XT_ZJTimer!
    var callBack: ((String)->())?
    var isMin:Bool = false
    
    init(seconds: Int, isMin:Bool, callBack: ((String)->())?) {
        self.isMin = isMin
        self.secondsToEnd = seconds
        myTimer = XT_ZJTimer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(timerRun), userInfo: nil, repeats: true)
        //如果希望对Timer做自定义的操作，使用_Timer属性
        RunLoop.current.add(myTimer._timer, forMode: RunLoop.Mode.common)
        myTimer.fire()
        self.callBack = callBack
    }
    
    deinit {
        myTimer.invalidate()
    }
    
    @objc func timerRun() {
        secondsToEnd -= 1
        if secondsToEnd == 0 {
            myTimer.invalidate()
        }
        if isMin == true {
            callBack?(minToTimeString(seconds: secondsToEnd))
        } else {
            callBack?(Func_HGT_secondsToTimeString(seconds: secondsToEnd))
        }
    }
    /// 秒数转化为时间字符串
    func Func_HGT_secondsToTimeString(seconds: Int) -> String {
        //小时计算
        let hours = seconds/3600
        
        //分钟计算
        let minutes = (seconds)%3600/60;
        
        //秒计算
        let second = (seconds)%60;
        
        let timeString  = String(format: "%02lu:%02lu:%02lu", hours, minutes, second)
        return timeString
    }
    
    /// 秒数转化为时间字符串
    func minToTimeString(seconds: Int) -> String {
        //分钟计算
        let minutes = seconds/60;

        //秒计算
        let second = (seconds)%60;

        let timeString  = String(format: "%02lu:%02lu", minutes, second)
        return timeString
    }
}

使用

import UIKit

import UIKit

class DemoView: UIView {
    var loveTimer:XT_IntimateLoversTimer!

    override func viewDidLoad() {
        //seconds根据实际计算（活动结束时间减去当前时间得出的秒数）
        if let applyEndTime = userModel?.apply?.applyEndTime {
                // 当前时间
                let timeInterval: TimeInterval = Date().timeIntervalSince1970
                let timeStamp = Int(timeInterval)
                let loveTime = (applyEndTime) / 1000 - timeStamp
                
                loveTimer = XT_IntimateLoversTimer(seconds: loveTime, isMin: false, callBack: {[weak self] (text) in
                    let contentStr = String("\(text)  后结束")
                    self?.timeLabel.text = contentStr
                })
            }
    }
}