Hello, Ashley,
You just described our favorite touring plan: take advantage of the morning Extra Magic Hours then hop over to a different park by late morning.
When we follow this plan, here is what we usually do:
From the Magic Kingdom, we like to go to Epcot since the monorail connects the parks (after transferring monorails at the Ticket and Transportation Center).
When visiting Epcot in the morning, we focus on Future World then head toward the International Gateway (located between the United Kingdom and France). We can then catch a boat over to Disney's Hollywood Studios.
When we begin our days at Disney's Hollywood Studios, we then take a boat to Epcot to explore the World Showcase (often making a late lunch reservation in one of the many restaurants in Epcot) since that is where you'll enter the park.
When our days start at Disney's Animal Kingdom, we often stay there longer so that we can have an early dinner at one of the
restaurants at the nearby Animal Kingdom Lodge. From the resort, we usually go to the Magic Kingdom for the evening. However, you need to do what you feel comfortable with. You may find it enjoyable to leave this park and go to a Magic Kingdom resort for lunch, such as the
Whispering Canyon Cafe at the Wilderness Lodge, then return to the Magic Kingdom.
Overall, I wouldn't worry about locking into a specific time to leave any of the parks unless you have a dining reservation. We usually play it be ear; it will become obvious when the park becomes crowded.
Please let us know if you have any more questions; otherwise, have an incredible trip!