Quit before you go home. Otherwise you'll be acting all weird and your parents will think something is wrong with you.

I wouldn't be concerned with going on the patch during finals or something like that. If you haven't been a "career smoker" then it tends to make you feel really really really good because it's basically a constant nicotine drip. I wouldn't start like the day of a test, but a week before or something (assuming you have the time) would be good.