How long after using my at-home teeth whitening kit can I smoke?

I have found the same question, but the answer wasn't definitive enough. I'm worried that if I smoke even an hour after I use the gel (it says to do so for 20 minutes) my teeth will instantly go completely yellow again, or be even worse because of the enamel sensitivity. I would like to know if it gradually reverses the effects of the gel (like it gradually strained the teeth in the first place) or instantly? If instant, how long should I wait for this sensitivity to go away?