Really, you need to do this in Javascript - AFAIK there is no way to do this from the server (there is no guarantee that you app is even running thirty minutes later).
And, I suspect that whatever you, it won't work in all browsers - IIRC Firefox won't let Javascript close teh browser window without user intervention.
Doing it in Javascript is easy:
http://www.java-scripts.net/javascripts/Auto-Browser-Closer.phtml[
^]