Here's what I've learned from a friend that ran last year.
Bikers start first, and 1 min later the runners start. The next wave follows 4 minutes later with the bikers followed by the runners, etc. If the first wave goes off at 6:45a, Wave 4 should around 7:30am. It's usually not an issue at all for teams to move back a wave if they want to run together. Team Beast would still be competing against other beast teams even if they moved back a wave - because teams will be ranked according to a chip time from a chip laced onto your shoe.
So it really doesn't matter when you start. The moment your shoe crosses the timing mat at the start line, and then crosses the timing mat at the finish line, that's your time. And it will be ranked against the other teams in the same class. The waves just help space people out on the course to alleviate congestion.