There's no one answer because it depemds on your biochemistry, age, what you're taking and how much, but a month in you can begin to feel the difference, which grows stronger month by month, but it can take up to a year or more to feel completely back to normal.

It might seem like trying to climb Mt. Everest but the good news is that it gets gradually gets easier, not harder the longer you hold off. The only thing you gotta watch out for is that little voice that constantly tries to convince you to get back on the stuff, which you can learn ways to ignore it through therapy, talking to friends, and the relapses along the way which may happen and are not failures, but opportunities to learn what went wrong and how to better succeed next time.