Really as long as you can (at least a day or so if possible). The issue is that if you are taking a drag on your cigarette, you can cause the clots that have formed to break up, and you'll start bleeding again. Not to mention a worse chance for infection.
You can't smoke for at least 24 or 48 hours. They should have given you a detailed list of what to avoid. Any kind of suction motion can cause the clot to loosen which can lead to dry socket. Apparently, that's very painful. I'm glad I never got that.