Following a bumping incident, airlines must offer passengers compensation at the airport on the same day. If the airline provides substitute transportation that leaves the airport before the airline can pay the passenger, the airline must pay the passenger within 24 hours of the bumping incident.
Can they bump you from first class?
Sometimes, yes. But not as often as economy, when talking about straight-out overselling seats. There are still plenty of reasons that you may be bumped out of premium class, or off the flight altogether: *An equipment change means there are fewer premium class seats than originally sold.