There are no hard rules against revealing your track early; I can't stop someone from doing a live-stream or anything. I do, however, think it's best to keep your mix under wraps until the music is all posted together.
I know all about Google Forms, but the ONLY way to guarantee that votes are legit are by keeping them on the forums. Someone could very easily dig up some old forum usernames of inactive people and ballot stuff that way. Given the things that have happened in the past with some competitions, I'm not interested in even dealing with the possibility of that. Plus I want people to sign up for the forums and get involved at OCR.