"Your room" isn't your room until you have checked in and received your keys, so there's no way to have something in there right when you check in, or any time before you check in. It would have to be delivered sometime after you have checked in. Now as to whether it could be done after you check in at the front desk but before you go to your room the first time (such as checking in early in the day and hitting the parks right away) that MIGHT be possible, but I doubt they would be able to guarantee it. This is in regards to using the Disney Florist. Any other packages you have sent to the resort would be held for you to pick up - they won't be delivered at all.