30 second timer

programming flash
1

I aneed alittle help please i made this small loader I need a code to add to this I made, That will stop in 30 seconds and go directly to next frame.

My As
onClipEvent (load) {
var rotateUnit = 10;
}

onClipEvent (enterFrame) {
_rotation = _rotation + rotateUnit;

if(_rotation > 100){
    rotateUnit = -10;
} 

if (_rotation < -100){
    rotateUnit = 10;
}

}

Regrads Barrie