I made reservations to day for next year for three studios. Can I link them today to MDE or does it take a day for the systems to update. Likewise, can I link the tickets as soon as the reservations show up?
You should be able to link the room(s) as soon as you have the confirmation number. You should make sure you have your Family & Friends list setup for all of the room occupants prior to linking the room reservation. If any of those have their own MDE accounts, connect with them prior to linking the room & tickets to MDE.
Linking park admission to MDE does not require that you have a room reservation linked.