I think it depends on the person and what dose they need and if the doctor guesses right.
I started on 10 mgs a day- supposed to see results in 2 days- nothing, increased to 20 mgs, nothing, increased to 30 mgs- better but not for 24 hrs. Increased to 40 mgs- relief. This was over a course of 2 months.
Now I'm being tapered- I'm down to 10 mgs and still doing pretty good.