We were there on a Saturday last month when the posted time for the MK was 10AM to 10PM. All of the big rides stayed open, but some of the smaller attractions and counter service restaurants closed around 6PM.
Among the early closings was everything on the River including the river boat, the railroad, Alice's Labyrinth, Storybook canal and the Nautilus walkthrough.
Some counterservice restaurants also closed around 6. As we were sitting down with our food in one of the CS we saw a castmember at the door telling people it was now closed. Walking around we saw other CS also closed.