Hi Christina ~
Making
Advanced Dining Reservations (ADRs) is always a top priority for me when planning trips to Disney World. All Guests (even those staying off property) can begin making ADRs 180 days prior to the date of their visit. Guests who are staying at a Walt Disney World Resort Hotel and have already booked their rooms, can begin making their dining reservations 180 days prior to the first date of their visit plus the next 10 days into their vacation. I don't know for sure but perhaps that is why T-Rex and Be Our Guest Restaurant were already booked up when you tried to make your ADRs beginning at your 180 day mark.
If you are unable to get reservations at your 180 day mark, I'd recommend that you keep checking every few days. If you haven't had success prior to your trip, keep checking even once you arrive on property. Guests will make dining reservations early and once their trips get closer and they start firming up their plans, they will cancel them which will free up some reservations.
You can also try walking up. There are also last minute cancellations for a number of reasons or they may be able to squeeze you in. If you want to try walking up, I'd try going just as they start to serve so it gives you the widest opportunity. We've been successful at some character dinning locations by walking up. Just be careful if you're trying to do this if you have little ones in your party that may be disappointed if you don't get in. If you decide to try that, you may want to send a "scout" ahead and distract your little ones' attention while you're trying.
I'll keep my fingers crossed for you!
Please feel free to visit us again with all of your planning questions. We are hEAR for you!
Wishing you minnie magical memories :-) Allison V.