AS3: Delay Enter Frame Animation

Question

I've got a fade out animation using ENTER_FRAME. I want the fade out to start after 2-3 seconds. How can I create this delay?

txtAlert.addEventListener(Event.ENTER_FRAME,animAlert);

function animAlert(e:Event) {
    if(e.target.alpha>0) {
        e.target.alpha-=0.01;
    } else {
        e.target.parent.removeChild(e.target);
        e.target.removeEventListener(Event.ENTER_FRAME,animAlert);
    }
}