Okay...I dug out my stuff from our trip in 2014, because we did this very thing successfully.
We had a 7:30 reservation at Hacienda de San Angel, party of four. We told the hostess that we would like a seat to see IllumiNations and were willing to wait for it. The lobby was really crowded and we did have to wait quite a long time. I don't remember when exactly we were seated, but the upshot is that with that 7:30 reservation, we did have a table next to the window and did wind up our meal just about at IllumiNations time. (We had appetizers and margaritas, as well as our dinner. There is a margarita with basil in it that was really great.)
The view of IllumiNations is very good. You can see it all, I think, but you are indoors, behind a window, and I personally think that something is lost seeing it that way. I would rather be outdoors for a fireworks show. We are going this September and will probably do something else to see IllumiNations.
(I'll edit to add that I notice your question isn't exactly about this. You apparently are figuring dinner will be over and you'll be looking for a spot outside somewhere. Maybe my post will help you figure on timing or something anyhow. Have fun!!)