Personally, I would suggest trying to get a couple of bar stools at the Tune In Lounge (in 50s primetime) and having a couple of cocktails and splitting a meal from the 50s menu. You can only order food if you are sitting at the bar. You can have cocktails at other perches throughout the lounge, but no food.
We did this on our trip last month on an early afternoon and enjoyed it. Additionally, the Echo Lake area is now beautiful and very festive with the huge Christmas tree and the large ornaments and decorations around Gertie. We got nice pictures at the beginning of November. The lounge itself should also be decorated for the holiday (wasn't done yet when we were there).
I'm not much of a fan of counter service at DHS. If Tune In doesn't work, I would probably choose to grab a table on Sunset Boulevard and find something to eat at Fairfax Fare or Rosie's. This way you should be able to see the projection show on TOT before going to JBJB. I think the Sunset Seasons Greetings starts when it gets dark and kind of runs continuously. Won't be sure until I get there in a week!!