It dosen't really matter what time you disembark: the shuttles run almost continuously and you don't need a reservation--that is just a convenience for you. But if you have to give them a time, tell them 10:00.
They use 7-9 passenger vans and the vans don't leave until they are full. But most of the people using the shuttles will be going to LAX so you shouldn't have to wait more than a few minutes.
Ask your porter to take you to the shuttle stand; thell the dispatcher there where you want to go and he will direct you to the next available shuttle.