Backers will be released for Prelyria based on their slots in Alpha or Beta. Players with pledges that grant them Alpha 1 access will be allowed to play VoxElyria first, followed by those with Alpha 2 access, then Beta 1 players, then Beta 2 players.
From the WIki page: https://chroniclesofelyria.gamepedia.com/Prelyria#Release_Schedule