It was less than two weeks for me, but that was back in the Fall of 01. Things are much different now. Some insurance companies play the stall tactic. Expect the worst, but hope for the best.
Haiziefrog, who is a drive-by poster
was approved in a matter of hours. So it is possible to get a really quick turnaround.
My only piece of advice I can give you is, to have all you ducks in a row. If your insurance company requires something (psyc-eval for example) have it done and include it with your packet the doctor's office will submit.
Good Luck to you!