In August, Wishes is typically at 10:00 pm each night so try for an ADR at California Grill about an hour and a half before. Reservations close to fireworks time are very popular and there are a limited number of window tables available, so there are no guarantees that you'll get a window table, but you can ask when you arrive for your ADR.
There is also an outside observation deck where you can go to watch the fireworks. I know when we haven't been seated at a window table, our waiter will ask if we want them to hold our entree until after the fireworks, and we've gone out to the observation deck to watch.
As for an ADR and table to watch Illuminations at the R&C, getting a table out on the patio is luck of the draw. I believe they discontinued requests for an outside table a while ago, but you can ask at the podium. If you do want to chance it, I'd suggest an ADR around 7:30 pm.