I will echo others - if you want Jack and Sally, I wouldn't do a sit down meal. Go straight to their line at 4 and last year they came out around 5. We did a Liberty Tree dinner at 3 pm on a party day and by the time we finished and got our wristbands, their line was crazy long. If you want only Dwarves, you could probably swing dinner. They do come out later than J&S but can't remember what time. If you don't care about either of those characters, then I would try for BOG at 4:15'ish but not much later.
ETA: or if you just want J&S, you could try an ADR about 5:30. I personally wouldn't do that but it's an option if you don't want Dwarves. We did a 2nd party and got to J&S line about 4:10. We were 3rd in line and were done meeting just a few minutes after 5.