Although listening back to what Summer said, she said they will be rehearsing the first half and went up to Christine's entrance and will go on (continue) after lunch, that does not sound to me like Christine does not come on till the end of act 1.
I wonder that's that thing in the background when Summer is on, It looks like a silver skeleton with a bit red something around the waist. You don't suppose that's something to do with the Christine-bot?
http://www.flickr.com/photos/27199361@N08/ Phantom at the Royal Empire Theatre