I used to be on 40mg a fortnight, but I had a flare up and was taken off it for a while, now i'm on 40mg a week, and although for a while I had bad dizziness and side effects upping the dose seems to have helped me.
However when it stopped working fortnightly, I did try a high dose of steroids first before I was put back on it weekly after a boost of 80mg in one go.
Most people I spoke to personally said it helped them within a month or so, but for me it tooks maybe three or four to see an effect.