Well, after 25 minutes on hold with no music (hang in there if there's no music!) I was able to book the 12/18 show at 8:15 and dinner at Marrakesh at 5:30 p.m. for a party of six.
Not what I had planned. I wanted the 6:45 show and an early dinner, but as another poster mentioned, that wasn't a possibility. The CM would only give me a dinner after 8:00 p.m. @ Marrakesh if we attended the 6:45 p.m. show.

Looks like the reservation system only allows AR times at certain restaurants for specific show times.

Maybe this is an attempt to stagger the CP reservation crowds?
Anywho--we adjusted so the little ones didn't have to wait a long time to eat. I guess we need to take naps that afternoon so they can last through the CP and Illuminations! The silver lining--we won't have to rush around between our dinner and the shows, so we can explore WS at night!
TIP: If it would be more convenient to pick up your package somewhere besides the main EPCOT entrance, it doesn't hurt to ask.
I asked if I could pick up my CP package at the International Gateway, since we enter the park there. The CM checked and said no, but we could pick up our package tickets up to 7 days prior from Y&BC instead. We're staying at the Dolphin (a non-Disney resort).
Good luck, everyone!