I'm at six months today. Looking back, I'd say the "acute w/d" phase for me lasted about 6-7 weeks, at which point the overwhelming sense of being totally dysfunctional began to ease up. By three months (12 weeks) out, I was beginning to feel better. Since then I've had windows, waves, and a long 6-7 week period where I was on an "emotional plateau" where nothing at all was happening - I was just in limbo. That phase ended a little over a week ago and I've been in a wave and right now I'm doing OK.
So, yeah, I'd say on average it's 2-3 months. Those who taper down to miniscule amounts seem to have a better time of it. I did a c/t from 5 mg. of Valium (I'd come down from 30 mg. in five months, cutting 2.5 mg at a time).