It's only a couple minute. You can view Illuminations from nearly anywhere on the circle. Is it character at dinner? Character meals take a good hour to 1.5 hours. You can finish quicker if you hit it just as the characters are coming to your area. Also, you may be seated after you reservation time. We were seated nearly 1/2 late for b/fast. If you really want to see Illuminations, then I'd move your ADR up an hour. If you don't care if you miss it, then stick to your time.