Longest I've waited so far is 9+ months. However, after a bunch of bull, I got my money back and told her to forget it. (You can read about THAT on my journal.) Three months is usually when I'd start to worry.
no i commissioned him at an anime convention in california, and hes just repeatedly made excuses like, saying that he had other commissions he had to work on first, i even told him hes had me waiting a few years now and then he promises to get it done but never comes through