how to close NSAlert after some time if no button is clicked by user

I want to close a alert Window (NSAlert) after specific period of time if user does not click on any of the buttons. Is there a way to set up a NSTimer to close the Alert Panel after some time, say 30 sec.

I just done something like that. I revised some of my codes for you here:

class ViewController: NSViewController {

    var progressWindow:NSAlert!

    func testOfProgressWindow() {
        progressWindow = NSAlert()
        progressWindow.alertStyle = .InformationalAlertStyle
        progressWindow.messageText = "some notes"

        let date = NSDate(timeInterval: 30, sinceDate: NSDate())
        let uiUpdateTimer = NSTimer(fireDate: date, interval: 0, target: self, selector: "closeSheet", userInfo: nil, repeats: false)
        let runLoop = NSRunLoop.mainRunLoop()
        runLoop.addTimer(uiUpdateTimer, forMode: NSDefaultRunLoopMode)

        progressWindow.beginSheetModalForWindow(self.view.window!, completionHandler: nil)
    }

    func closeSheet() {
        self.view.window?.endSheet(self.progressWindow.window)
    }

}