It doesn't take long at all. The feeling they provide just makes it too easy to abuse.
I went from 1mg of xanax xr, to 2, to 3, and currently on 4mg/day over a course of the last year. 1mg of xanax XR used to knock me out within 20 minutes. Now I can take 4 mg at once and I get that "good" feeling that 1 mg used to give me, and it's not even as "good" as it was with 1mg back when.
I'm definitely dependent/addicted to it at this point. I dream of having piles of xanax pills on my desk, similar to the mountains of cocaine in the movie Scarface... I'm sure that isn't a good thing but I laugh at the thought at the same time. Ha. Seriously though, it only takes a couple hours past my usual time and I start getting the sweats and it goes down hill in a hurry.
The goal of my benzo use was to get me to do stuff. Go outside, go to stores, go back to school, etc. Get "used" to these things, and then slowly taper off benzo/keep use to a minimum. It definitely eased my anxiety, but I didn't push it hard enough in the beginning to really "get out."
I think I waited too long to "test" my Xanax. I should have started school last winter (January), however, I'm going to give school a go in 4 weeks. If it goes well, I'll continue to take it and probably continue to get higher doses until my p-doc sets the limit. If school doesn't go well, I'll start the taper down/withdrawal process and go from there...