IIRC, Pre-Pay is pretty much always open... Since event / character / player needs to be noted on the prepay thingamajiger, pre-pays can be accepted as soon as there's an event scheduled.
Pre-Reg probably ends on Friday the 15th, as that is a week before the event's start time and is the last weekend before the event.
Though, I could be wrong, as they've gone back and forth between closing on the Friday and Monday before the event...