I've always done airbrush, and loved it. However, if you want full color, I wouldn't do it more than two or three days before your competition. I normally would go on Thursday if we were leaving Friday, or Friday if leaving saturday. I learned very quickly that you should shave before you go, and not to shower for at least 12 hours. They always say 4-8 hours, but my color always looked best after I waited longer to shower. I never ruined or even got dyes on any clothes. What really stunk for me however, was that I have several skin diseases, so I have really itchy skin like always, but especially when I can't properly moisturize. Airbrush tans are notorious for seriously drying out skin. If you get an airbrush, I heavily recommend also buying the Norelco (sp?) lotion that's meant for airbrush. It was like finding water in the desert after waiting 12 hours, lol. Oh, and the lotion progresses the color more!
Make sure you never, ever, ever do Mystic Tan. Just. Don't. Do. It. An old teammate did it before we went to the Summit in 2013, and fell asleep afterward, with her hands on her legs. Hand prints. on her legs. It was so funny. DONT GET MYSTIC