Hi, Kristy! What a wonderful place to be when celebrating a birthday! I hope it turns out fabulous!
The In Room Celebration - or any other delivery that you may opt to purchase - cannot be delivered until after you've physically arrived at the resort. Once you are all checked in, have your keys in hand, and are ready to get your vacation started, then they can deliver items to your room.
It would be a lot of fun to arrive to the celebration, but it really will just add to the excitement to come back from a fun day or evening at the theme parks and find the room has been magically transformed by Mickey and Company! But the fabulous Disney florist wants to make sure they are delivering the celebration to the right person, so they won't deliver until you have officially arrived!
In case you need the information handy, the In Room Celebration, along with dozens of other delightful surprises, can be found at the Disney Florist website, located
HERE.
Have a wonderful vacation!