I made our ressies for 4:00pm so we will be in the first batch of dinner guests, and hopefully won't have to wait too long to be seated.
Then again, last year we had 11:35am ressies at LeCellier (first time slot available during lunch) and arrived early as instructed, and still had to wait until Noon to be sat. So one never knows with Disney, but it is safe to say that you'll never make Illuminations in time. Sorry!