Change Login Cookie

I’m designing a blog that will mostly be used by people on shared computers, and all of them will have to post (they’re police officers in their cruisers — mobile intranet — if you are really interested). Therefore, the normal way that WordPress administers cookies is inadequate, because teaching people to logout is harder than you might think. Is there a way to set a shorter time for a valid cookie (i.e. 10 minutes), or make it so they always have to login (never saves information)? Also, could I add a check box somehow to allow it to save the login information (for those that do not share a computer — this is less important though)? WP 1.5

Thanks.