Why does this script just quit and not countdown first?

I am using this count down script to auto quit when it counts down to 0

It counts down in the play mode and after i build it quits as soon as the game starts ?

Any ideas why

Thanks

#pragma strict

var timer : float = 60.0;

function Update() 
{
	timer -= Time.deltaTime;

	if(timer <= 0)
	{
		timer = 0;
		Application.Quit();
	}
}

function OnGUI()
{
 	GUI.Box(new Rect(10, 10, 50, 20), "" + timer.ToString("0"));
}

You should have a look at Coroutines instead, they are perfect for this =)