You've got a few options to consider you want to stay off the site:
You can download a personal site blocker like StayFocusd and add GTPlanet and any other sites that are keeping you counter-productive. This way you won't be able to access them at all. I did this during my exams last year, as well as blocking other sites like Reddit and the book of many faces.
Another way is to change your password by sporadically flailing your arms at your keyboard and then logging out. You won't know what your password is, so you can't log in. While you won't be able to post in the forums, you'll still be able to view them. Once you want to return again, simply click 'Forgot Password'.
If it really means that much to you to have a 1-day ban (although I fear it would probably be longer) then PM a moderator. If they're feeling generous they might do it. Trying to get yourself actively banned on the public forum is just irritating and will probably end with something more long-term than you planned.
The real funny part is when they forget after a week or two that you're still under a ban. Oh the laughs that the user who asked for a 24h ban will not have.