The first is that only 1 of the 2 major attractions will be open. The Millennium Falcon: Smugglers Run attraction will be open at launch, while Star Wars: Rise of the Resistance will open later this year.
The second is that, for the first month of opening, guests to Disneyland’s Galaxy’s Edge will need a free advance reservation, subject to availability. Millennium Falcon: Smugglers Run won’t be part of Disneyland’s Extra Magic Hour of park mornings, although it will be at Walt Disney World in Florida. Initially, the Millennium Falcon attraction won’t even offer Fastpass service (Fastpass at either park, Maxpass, or Fastpass+).
It sounds like Disney Parks know how much demand is being built up for this experience and wants to keep crowd interest from turning into an avalanche, while keeping things as fair as possible for every guest.