I never saw an inspector in the 3 years working in a panel shop.
As for the running costs, they go up when you have the burners on. Most of the time you only do that when you're trying to pump jobs through the booth fast. Nothing wrong with painting a job and leaving it overnight to cure. The painter at our shop used to do all our personal stuff on a Friday arvo or Saturday and then we'd come in early on Monday and help him unmask and get it out of the booth before start time.