We did this last year, and I made an ADR for 7:20. I think your time may be a little late because by that time, anyone who has intentions of watching Illuminations will already be seated...and they will not leave. We requested a table on the patio for viewing as did the couple behind us(at check in). Both of us got seated on the terrace thingy on the side of the restaurant. We couldn't have seen the show well from where we were seated, but it was a nice table and at showtime the CM escorted us to the lower patio area(this is common practice). We had a great time!
OH....as far as the food goes, we were all very pleased. I loved the Bangers and Mash and I don't remember what the rest of them had, but no one was unhappy. We were, however, disappointed somewhat in the Sticky Toffee Pudding....this stuff is way overrated, IMO.