Pop under delay script - repost

I need a simple piece of code that will run a .js 25 seconds after the page is closed. Basically, I would like to keep the user from realizing that pop-under came from their visit to my site -- also, only one popup per user per month. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Installation package that will install the software (in ready-to-run condition) on the platform(s) specified in this bid request. 3) Complete ownership and distribution copyrights to all work purchased. ## Platform php ## Deadline information need to test code before payment is made -- must work in all browsers above 4.0