I think 6:30PM is just right... though of course it depends on several things:
1. Server- how fast/slow they are
2. How big your party are- if it's 2 people, you'll be faster; if it's a family of 6, well, expect more time
3. What you order- if you eat your steak well done, expect to sit in the restaurant for longer. Table next to us were seated when we arrived and had their appetizers, but because they ordered their steak well done, their entrees arrived when ours did (we have ours rare).
4. How much you order- appetizer, entree and dessert? Expect 90-120 min. Just an entree? You'll be out in no time.
5. The wait- crowded day, even with an ADR, expect to wait.
We ate there last week. ADR was 7.00PM but we didn't get seated till 7.15PM and we showed up early. Didn't get out till 10 min before 9PM. Most good spots for watching fireworks were taken.