Oh, the contestants are there for a long time before the show first starts getting their first numbers ready.
I don't know if the stories are true, but I do think things are not as authentic as the viewers are led to believe. Some years the scoring has been so horrific that is was comical. And it was obvious the judges were bound and determined to get some good dancers out of there, so their pet could win. I do believe that. (Recall the Karate Kid?)