never take more than 500mg of niacin a day and a b12 as well as drinking alot of water. Metabolism, body makeup(fat content) and smoking frequency have alot to do it with it. If you smoke once a week and you are athletic, exercise at least 3-5 times a week and have a good metabolism which you should if you are in shape it won't take longer than 7 days to be clean even for the most sensitive test but most general tests will come up clean after 4 days.
I only use azo standard right now because it is extra security for me after smoking just in case but otherwise you should be able to clean out naturally.