How often and how much do you smoke? They say your typical smoker (which I'm guessing means a few times a week? I don't know all my friends are total stoners) is around 30 days.
When I got my DUI and had to do out pateint drug treatment you couldn't move to level 2 until you totally passed a piss test. I was a really heavy smoker at the time and it took 47 days to be totally clean.
Like some already said though there are lots of things to take into consideration. If you took a few hits of weed 2 weeks ago and hardly smoke you probably are already cool.