That depends on which "cravings" you're referring to. Nicotine leaves the body, on the average, in 3-7 days (you can speed up that process by drinking lots of water or fruit juice and by exercising--with a doctor's supervision, ideally). That should take care of most of the PHYSICAL cravings, which are generally the worst; but then there are MENTAL/ EMOTIONAL/ BEHAVIORAL 'cravings' that you may have to deal with as well. These urges to smoke can appear, occasionally and unexpectedly, for months or even years after you quit. The good news is that, depending on how much work you're willing to do, or on how strong your support network is, these unannounced cravings can usually be dismissed quite easily and quickly. Many ex-smokers never again experience the urge to smoke.
Afraid of the withdrawal symptoms? Nicotine withdrawal is uncomfortable but not life-threatening. Irritability, nervousness, difficulty concentrating, increased appetite, and urges to smoke are short-lived. Nicotine withdrawal is the worst 1 to 2 days after quitting and only increased appetite and urges to smoke typically persist beyond a couple of days.
Afraid of weight gain? On average, smokers who quit gain approximately 5 to 10 lbs., well worth the health tradeoff from quitting. If you are concerned about weight, recent studies show that those who manage their diet and exercise while quitting smoking not only minimize weight gain but also increase their chances of quitting.
Afraid of failure? Quitting is a process that usually takes many attempts. Smokers typically attempt to quit four or five times before quitting for good. Prior attempts are not signs of failure. With each attempt, you learn more about your nicotine addiction and how to handle the quitting process. The fact that you've tried to quit before is likely to be a positive sign that you can quit smoking the next time.