Can your gums turn pinkish again if you quit smoking? if yes, how long would it take? if no, why?

Maybe: The color of your gums or gingival tissues is affected mostly by genetics and to some extent by local issues such as amalgam tattooing and cigarette tar. If you are smoking enough to discolor your gingiva, please do your best to reduce this habit mostly for your health. Brushing your gums after quitting will help but you may need additional treatments to alter the color.

Yes: I'm assuming they are not pink because they are infected, ( usually seen as a reddish color) smoking causes infections in the mouth by altering the bacterial population. When you quite smoking, assuming you are just doing healthy things your gums should start getting better so in a few weeks they should look much better. Congrulations on stopping smoking!