What time does rdu open?

To my knowledge it doesn't "close". Shops do close and open, but it's undergone and continues to grow fairly rapidly. Its not LAX by any means but it's a large airport. If your waiting on a connecting or delayed flight they won't kick you out. If you want to arrive early for an early morning flight, I'd say arrive and be parked 1 hour before boarding given that it's Christmas. But personally I arrive about half and hour before boarding time.

I think doors are open but you should check with the individual airline counters to see when they open. TSA opens at 6am