Change z-index after few seconds?

Hello,

So I am making this web page where I have an SWF banner overlaying HTML content/div.
I have set the div which contains html to z-index:-1 so that my banner can overlay it when the flash animation expands.

Problem is after the swf overlay is done and it goes back to it’s smaller shape the html content is still not selectable, since the swf is on top of it.

Is there a script or any method I could use you fix that?
Thanks