We did it for our Dec. stay. When we got there at 12:00 pm, they did have two CM dealing with online check in and a line for everyone else. However, I have read that others have gone to check in and were kept in the same line.
I don't think it saved me that much time, but my room was ready. I did not get my request, but didn't even ask about it when she said the room was done as that was more important and we were only there for two days.