2 weeks. That's about how long Accutane takes to get out of your system, and by then it's at very minminal levels if not already gone.
Techincally, you still can drink even while on Accutane, but it's increasing it's effects and isn't a good idea, and puts extra strain on the liver, but I guess some people still do it. Still not a good idea though, so good thing you aren't doing that.
I'd say even a week after being off Accutane you can drink a little bit, just don't over-do it. Accutane will be at much lower levels in your body after being off it for a week, so you probably can drink some and be fine. By about 2 weeks after being off Accutane, you'll pretty much be nearly at the same point as pre-accutane. By 3-4 weeks you can pretty much drink as much as you used to before ever being on Accutane. Perhaps even after 2 weeks, but there still may be a little left in your system.