They have times throughout the day, and I think each one lasts maybe 10-15 minutes? We were there this past December, and managed to only catch part of Father Christmas in the UK. I was kind of bummed, because I had hoped to see most of them, but it just didn't work out.
Make a point to stop in at the American Adventure and go inside to see Voices of Liberty perform in the rotunda. They're all decked out in Dickensian costumes and they sing Christmas and Hanukkah songs. Absolutely beautiful!
Oh, and if you can catch "Joyful" on stage over on the Future World side, they're a great gospel group with a ton of energy! My 73-year old dad loved them!
Decorations abound. It's truly magical.