Settling in at school - Nursery

This is my first post. Found you after searching for a conducive place for my ramblings.

I am a mother to a 4 year old diagnosed with ASD. He is becoming verbal and speaks but drops his consonants. He was in nursery and now started in a mainstream school with a statement and a 1 to 1 teaching assistant for 25 hours a week.. We were told to come in for an hour to settle him in and school now seems to think that he should only come in for an hour a day and have no plan set up with no end in sight. He was in nursery for 3 hours a day and settled nicely. He got potty trainied in the summer and goes happily now for a wee. Still struggling with the poo, but one step at a time 

When I picked him up after his first hour, he cried when I said it was time to go home. He was a bit overwhelmed but I feel an hour was nowhere near enough time for him to settle down. Not sure what to do now as I do not want to start a new school fighting, I fight well!, but just want to give them a chance. My son is not rigid, not bothered about routine, eats anything, likes playing outside and does listen to most instructions except when the sensor overload gets too much and then a little trip outside is all he needs to calm down or a little distraction. His main problem is his speech delay.

Please help. I am so stressed and do not want him to miss out on his settling in time. One hour seems so little. Anyone had any experience to share with me, please? I would appreciate any help at all. Kind regards