I tried it for six weeks, but never got it to settle down into a reasonable schedule. I'd have a few days of pretty good sleep, followed by a hard crash, then a struggle to get back onto the schedule etc. Especially falling asleep quickly was very difficult for me (whereas I fall asleep very easily on a normal schedule).
From what I read, it took quite a long time. Between one and three months, depending on the person. I guess three months would be pretty painful. I've never tried it personally, so...