I thnk there are few issues. One, our experience getting seated at Garden Grill was terrible, we probably waited close to 45 minutes after our ADR before we seated. With a late ADR like that, they will probably be backed up at least a little. Two, you are really going to have to rush through the meal to eat and rush out to see Illuminations. Three, at the earliest you are probably going to leave the restaurant at about 8:45-8:50, at which time you are going to have a very hard time seeing much of Illuminations anyway (except the fireworks that go up in the air) with all the other people lined up in front of you.
I would keep trying for a much earlier time or decide whether you would rather do Garden Grill (and take your time to enjoy it) or catch Illuminations. I think with the 8:10 reservation, you may end up rushing through the meal and not enjoying it - and then rushing out to Illuminations and not really enjoying it either since you don't have a good view.