How long, after you quit smoking, does nicotine stay in the bloodstream?
Medically the nicotine is gone in 72 to 96 hours unless you receive it from second-hand smoke such as bars, closed rooms, etc.
It will take your body much long to get over the effects of long term nicotine addiction
But the benefits begin immediately: Carbon Monoxide levels begin dropping, Blood pressure drops.
See
How Fast will I recover and is it worth it?
Now this is generally speaking... each person will be different. So if you are still smoking on Wesnesday, do not be surprised when nicotine shows up in your blood on Friday.