Hmmm... I can tell you first hand, painters and artist-type guys are generally flakey, and hard to keep on a schedule. My guess is that you will get your paint job back in triple the time you expected but the quality will be really high. They have a knack for doing things like that.
We had a car painted once that was supposed to take a month. It took over a year, but the results won the Chicago Hot Rod World of Wheels Best Paint 3 years straight. Go figure.
Keep hounding him. Once a week, then once a day. Tell him you are going to call him every day until he gets it done. They hate that the most, and want to get you off their back as soon as possible. He'll paint it right quick.