The NSTimeInterval value of this property indicates the seconds from which the date picker in countdown-timer mode counts down. If the mode of the date picker is not CountDownTimer, this value is ignored. Maximum value is 86,399 seconds (23:59)

let datePicker = UIDatePicker(frame: CGRect(x: 0, y: 0, width: 320, height: 200)  
datePicker.countDownDuration = 60 * 60