This demo will show you how to put a delay before initilazing the flex application:
In the source of his preloader.as...
private function onFlexInitComplete( event:FlexEvent ):void
* If the Flash MovieClip is done playing it's animation,
* I stop it and dispatch my event letting Flex know I'm done.
* @param event
private function onDoneAnimating():void
dispatchEvent( new Event( Event.COMPLETE ) );
He waits for an event - but you could put a timer in there if you wanted to have a set amount of time to wait.
Mark this as an answer if it helps out