Your Monday MK day has me confused. If the park opens at 8, you'll only have about an hour before you need to leave for your 1900 ADR. If it opens at 9, you don't have any time at all. Then after breakfast, it's time to go back to the room. What is your thinking on that day?
HS could still be a good choice for your arrival day, depending on the age of your child. I know they can do Toy Story Mania, and there's all the shows to see. It could be a relaxing step into the parks after your travel.