How long does it take for nicotine to leave your body (urine and blood stream) after you've stop smoking?

It varies: Nicotine metabolism is complex. Most nicotine is metabolized in the body to co-nicotine, and this is what is tested for. Nictotine is 1/2 gone after 2 hours, co-nicotine about 20. It takes about 5 1/2 lives for a drug to be "97% gone". 10 half lives for 99.9% another source says a urine test can be positive 7 to 20 days after smoking.

24-48 hours: Nicotine is a very short-acting drug and is metabolized quickly, which is why people who smoke have a cigarette generally at least once every 45 minutes while awake. However, its metabolite cotinine lasts longer, and can be detected for about 2 days after quitting smoking. It depends to some extent on whether you are a half-pack/day or a 3-pack/day person, but usually 48 hours is adequate.

Nicotine: Nicotine will slowly leave the body over 3-7 days.