I think it is not difficult to adjust because whatever new time that you intro to him, he will eventually get used to it. Say, he wakes up at 10am (hopefully late because he will skip nap). Then you only need to give him light breakfast followed by lunch, probably 12plus so that he can be at school by 1pm. This depends on his speed of eating and distance to school which takes up travel time.
After school he might be slightly tired but you can keep him occupied with activities. Try to put him to bed early as possible, maybe 9pm.
I think you can start this schedule 1-2 weeks before school reopens and train him to drop his nap.
In his bag, you just need a water bottle. You can pack light meal like cereal or bread because PCF will have snack time in between the 4-hour program. Having said that, you can still encourage your child to take school food because they might cook porridge, macaroni or similar food. Other that, he will carry Communication Book to scgool daily. If your child is already fully toilet train, need not worry about accidents. Otherwise, you can pack extra set of pants.
dont't worry at all because there are many other K1 students who is in 1-5pm session and able to skip their nap. Good luck!