We were there last year in early November (Jersey Week) under similar circumstances. We went on our last day, I think, which was Early Magic Hours. I participated in "the Running of the Dads" at Rope Drop and my wife and daughter caught up a few minutes later (it was our only morning at Magic Kingdom and I didn't want my daughter to miss the show).
If I recall correctly, Elsa and Anna didn't arrive until around 8:30, and from that point, we had about a 15 minute wait. I'm pretty sure were were done and on another ride by 9 am. Not a GREAT way to spend the Extra Magic Hour, but it made my daughter happy.
Now, if you're going Christmas week, the crowds are going to be much, much worse, but first thing in the morning is still probably your best bet.
My understanding last year -- and I don't know if this has changed -- has that only one member of the party needs to be on line to wait, so theoretically, one adult could entertain the kids while another waited on line (ah, cell phones -- what did we ever do without them?). When we went last year, we were joking around with the people in front of and behind us. The guy in front of us had been sent ahead by his family WHO WERE STILL AT THE HOTEL! When we got the the "inner hallway" (where there are paintings of all the princesses) he pulled off to the side and started letting everyone go in front of him. When we parted company, his wife had just called him to say they were arriving at the park.
One thing to keep in mind is that the Rope Drop at Magic Kingdom is madness like something out of a movie. A herd of people, mostly a wave of dads, grandfathers, and older siblings, stampedes down Main Street, led by a human wall of Disney cast members. Folks who try to cut through the main street stores to get ahead are bounced back out. When we got to the end of Main Street, I think everyone thought the human wall would break down, but it kept going right up to the entrance to Cinderella's Castle. Then through. Once on the other side, everyone started drifting right, trying to get to Elsa and Anna, but that route was blocked, and instead we were led the long way around the Carrousel before finally being "released." Every time we reached a juncture and the cast members didn't break away, and increasingly large number of parents would yell out things like "Come on!" It was frustrating, but also laugh-out-loud funny.
