When we went to LC, February of 2007, we had 7:15 reservations, and I am pretty sure we did not get in until almost 8pm. I would not count on getting out on time.
I'm with MinnieLovesMickey thinking you might want to consider Rose & Crown. I think it is one of the most underrated restaurants on the property. The atmosphere is so friendly and relaxing, especially after a long day at the parks and they time everything really well so that you can go out and see Illuminations from their patio, if you are not able to score a patio table. (Personally, I prefer eating inside for that Pub atmosphere!)
We did really enjoy LC as well, but if it is your only chance to catch Illuminations, I don't think it is worth missing it for.