This is just a elaborate version of @mike’s solution
#pragma strict
var time:int=0;
function Start () {
time=100;
InvokeRepeating("countDown",1f,1f);
}
function Update () {
}
function countDown()
{
time-=1;
}
function OnGUI(){
var minute:int = (int) Mathf.Abs(time/60);
var seconds:int =time%60;
var labelString: String=minute.ToString("00")+":"+seconds.ToString("00");
GUILayout.Label(labelString);
}