If you really want to pause and later on restart the countdown from where it stopped you have to store the date:
1) In CountDownClock add a private variable:
private var _date:Date;
2) in the init() function initialize it right before starting the timer:
_date = new Date();
3) Adapt your onTick() method like this:
public function onTick(evt:TimerEvent):void
{
_date.setTime(_date.getTime() + 1000); // increment with one second
// updates the clock display
this.text = getCountDown(countDownDate.getTime() - _date.getTime());
}
But once again, once you have paused the countdown, restarting it will never give you the correct result.
Since pausing the countdown doesn't mean the time stood still.
Its your choice which implementation you want.
