...Convention Schedule... those who pre-registered for the convention may pick up
their packets on Wednesday the 18th between 9am and 4pm.

Those who did not pre-register may register (and I assume this means to buy a one-
day admission pass) on Thursday the 19th beginning at 8am.

The convention floor opens at 9am on Thursday to those staying at the Riviera -
and at 10am on Thursday to those not staying at the Riviera.

That's my understanding of the sequence of events.