NSDate 最大最小时间配置

let currentCalendar = NSCalendar.currentCalendar()
        let dateComponents = NSDateComponents()
        let timeInterval = datePicker.countDownDuration
        
        let SecondsPerDay     = 24 * 60 * 60
        dateComponents.second = 3 * SecondsPerDay - Int(datePicker.countDownDuration) - 1
        let threeDaysFromNow  = currentCalendar.dateByAddingComponents(dateComponents, toDate: datePicker.minimumDate!, options: nil)
        datePicker.maximumDate = threeDaysFromNow