It has been a number of years now, but when I was there at Easter time, the crowds at MK grew as the morning progressed, so by around noon it was really packed. We went early, left around mid-day, and then returned early evening. With scheduled fast passes you might now be able to extend a morning visit pain free by using lines for attractions at first, and scheduling the fast passes for late morning/early afternoon.
Some school districts schedule off the week after Easter regardless of how early or late it is, while others opt for a certain week, like the second week of April every year, and then there are all sorts of variations in betweeen!