There will be a grace period after the 24th for Pre-order customers to keep playing until they get their retail boxes. No worries that you'll be left out if you don't have box in hand.

Open Beta players will not be able to play past the 24th, however. If they wish to play past launch, they need to Pre-order or buy the game (but only those who Pre-order get to keep their characters into Live).

-Meghan