The school my two go to / will go to start them off at 8:45am on the first day of term. Off they go, straight in, everyone the same, full time from day 1.
The odd parents requests part time and there are options for this but we are told that it is fairly rare and that, on the whole, they find kids settle better if they start full time.
My son is just 4 and understands his life at the moment. (Some days he goes to nursery, some days he doesn't, some days he is picked up early, some days he isn't, it is all very carefully worked out.)
He will understand - "on Wednesday you start school, you go every day except the weekends, just like Dd and Mummy will pick you up on X days and daddy on Y days."
He's a bright lad but I think he'd struggle with "On Wednesday you start school. Here is the complex 6 week time table, sometimes you will start early and finish early, sometimes you will start late and finish late, it will,change each week, the kids you are with will change each week and we have set up a very complex system of different strangers picking you up each day as we don't have the holiday to do it ourselves and no childminder is willing to give a full time space to a child for just 6 weeks."
Add to that I really really think that my (limited) holiday is best used to give him a lovely peaceful half term at home with me, rather than him having to go to holiday club because I've run out of holiday.