Take whatever time you can get! (We've nvever been so lucky as to actually get a choice of times, LOL).
Even if you are staying off site and get an early time, you will still be able to get into the park on time to make the PS. You may need to give your name and confirmation number to the CMs at the TTC, but you will not be the first, last or only off site people to eat early at the MK restaurants.
Best wishes -