[Zebestov]

var timer:Timer = new Timer(1000, 600);
 
// добавляем это ////////////////////////////////////////////////
timer.addEventListener(TimerEvent.TIMER, onTimer);
function onTimer(event:TimerEvent):void
{
	myTextField.text = getBeautifulCount();
}
/////////////////////////////////////////////////////////////////
 
timer.start();
 
function getCount():uint
{
	return 600 - timer.currentCount;
}
 
function getBeautifulCount():String
{
	var count:int = getCount();
	var m:String = String("0" + int(count / 60)).substr(-2, 2);
	var s:String = String("0" + (count % 60)).substr(-2, 2);
	return m + ":" + s;
}