I don't recommend it because it would affect your attendance. You say you don't care, but honestly, you should. It's year eleven so it's the year that employers are going to enquire about the most and if they see that you're taking days off for seemingly a minor reason, your chances of getting the job decrease dramatically. Also, ask yourself how much work you would actually get done. It's only six extra hours of work so why don't you just do it when you get home from school?