We had a 7:40 ADR a couple weeks ago and showed up about 7:15 (our "strolling the grounds of the Grand Floridian" plan was rained out). Wishes had been scheduled for 9 but got pushed to 10 right before we left. We were seated about 7:20 and finished dinner about 8:50. We had bread, entrées with wine, and dessert with tea (if that helps you plan how long it will take).
We were going to boat to the MK to try to catch the end of SpectroMagic, but instead ended up having to dock at the Poly to watch the Electrical Light Pageant go by, then got to the MK at about 9:30--exactly on time to grab prime seating at the train station to watch Wishes. The best laid plans, etc.--it worked out so much better than my original plan.