what about Crystal Palace, Liberty Tree Tavern or The Plaza...all in the MK, and all three show availability in the 4:00 to 5:30 range. Of the three, for dinner I'd prefer Crystal Palace myself - good buffet, lots of choices. 2nd choice would be The Plaza, although the menu is limited to sandwiches, they are very good & ice cream goodies for dessert! Liberty Tree would be my last choice -- it was good food, but not all that special. And though 4-5:00 seems like very early to eat, it actually is a very good time to eat before a party...you want to be long done before 7:00 p.m., and INSIDE the park before the party starts.
That's what we did last year, ate at CRT at 4:10. We knew we were eating early dinner, so we had a big breakfast, and just a snack at our usual lunch time. Then into the MK at 3:30 to head to the castle. It took just over an hour from check-in until we were out. Then we were able to go over to the Rose Garden and get our tickets scanned, get our wristbands, maps & treat bags. We were then able to do a couple of rides before the party started and we were ready! Doing it that way, no long lines outside the park to get in for the party because we were already there.
If you're not planning on using a regular park ticket that day (just going on your party ticket) then you can probably get into the park on your party ticket at 4:00...that's the way they've done it in the past) so get a dinner reservation for around 5:00 to allow time to get into park and back to the restaurant.
Kona & The Wave are both good, too, but you only get a 3 hour parking pass for dinner reservations there. If you want to leave your car longer, you'd have to pay to valet park (cost you $12 to valet, plus a $2 tip when you pick up car.) And, not starting until 5:00, take an hour to eat and then another 15-20 min. to monorail to park, go through security and then get your park wristband, etc...you would barely get into the park by the start of the party especially if you encounter long lines of party-goers arriving between 6 & 7 p.m. at the park entrance.