Hello Amy!
First off, great choice going to the Walt Disney World Resort during the holiday season. All of the Parks and Resorts are beautifully decorated and the mood is so festive during this time.
In my experience, no matter how close to closing your dining reservation occurs, you will have all the time you need to enjoy your meal. We have never felt rushed even with the latest reservation of the day. Additionally, while Epcot's closing times is listed at 9:30 pm, you may notice that
IllumiNations:Relflections of Earth, Epcot's firework spectacular, doesn't begin until 9:30. This fantastic show is approximately 15 minutes long during the holiday season and is a must-see. With that said, most people won't even begin to leave the Park until close to 10:00 pm. If you don't have a viewing of IllumiNations: Reflection of Earth already planned I suggest taking a pause during your meal to step out and see it. We did that not to long back at Le Cellier and the Cast Members serving us were very gracious about holding dessert until we got back.
I hope this helps with your planning. See ya real soon!
Anne