Although R&C is one of the faster places once you are seated, you should be fine since R&C stops seating before IllumiNations. I think most nights when the show is at 9:00, the last reservations are about an hour before that. A 3 course meal there takes about an hour.
When you check in you can request a patio table, but since many ask for one you may or may not be accommodated. You might be able to wait, but if it is busy, many parties have already made the same request and are waiting or they are not taking requests that evening, you will be seated at the first available table for your party size. The good thing is R&C has a viewing area adjacent to the patio just for their diners so if you are seated indoors or at a patio table without a view, let your server know you want to see IllumiNations and they will pace your meal accordingly.