As some others have posted, I think there's a real good chance they add them on Sunday. I don't know why they don't just schedule it that way to begin with, it would save a lot of grief. We went the first week last year and checked in on Saturday and there was nothing scheduled for the week. I don't think we even found out about adding the Sunday until Sunday morning. When they do stuff like that there are lots of people who don't realize they have updated hours unless they happen to be at MK that day anyway.
I hope it's not as hot for everyone as it was last year. I think it was mid 90's the first week last year.