Hi Amy,
Cinderella's Royal Table will make any guest feel like a princess! It truly is a special treat.
Are you planning on attending Mickey's Very Merry Christmas Party that is being held that evening? This is another amazing way to spend the holiday season at Walt Disney World, so I highly recommend it. If you're not attending, the park closes at 7:00pm for regular guests, so I would recommend making plans to dine at Cinderella's Royal Table on a different night.
If that is the only night you have available for character dining. You might consider dining at 1900 Park Fare.
Cinderella's Happily Ever After Dinner is excellent. You could make a 7:30 reservation and then head out to the beach of the resort to catch the fireworks. Also, it only requires one dining credit!
If you are attending the party, I recommend dining any time before 7:30 (earlier is better). It usually takes about 90 minutes from the time your name has been called to the time you exit the restaurant. At least that's been my experience with character dining. That should give you plenty of time to see Holiday Wishes and the second viewing of Mickey's Once Upon A Christmastime Parade.
Your credit card is used only to hold your reservation. It will not be charged unless you fail to show up for your reservation without cancelling.
Hope this helps. Have a magical vacation!