Nicotine doenst last long, maybe 1-2 days. Now the by product Cotinine can last for 7-14 days, depending on your smoking habits.
http://www.fbr.org/publications/pamphlets/cotinine.html
This site say ten day, but Id say two weeks to be conservative.. Also keep in mind if you die because of a smoking related death, the insurance company can deny or alter the final end dollar amount they will pay out. This is only if you checked NON-smoker on the application.