Site browsing time limit

Does anyone know a plug-in or javascript or some other hocuc pocus that will allow the user to browse a site for a certain amount of time then stop them looking at anything else? Ie they get 10 minutes free time as a trial run but after ten minutes every time they try to browse a page on the site they get redirected to a sign-up page or just shown a message saying their time is up. Any suggestions welcome.