No special day for him. I think "go early and leave early" MAY work for you?
There is no special day, but I would check a crowd calendar for a less crowded day. Visit guest sevices upon entry for the various services they provide to help your child tolerate the crowds. Headphones or earplugs with noise cancellation can also help with anxiety. There are less crowded pocket areas where you can go to for tantrums. Be sure to ask any cast member to show you the quiet places.
There will always be crowds but you can book a character breakfast early and when there aren't too many people
Thanks! Your answer is awaiting moderation.