4K is not required in any state in the U.S. It's impossible to mess up something not required. I don't know what country you are in - if it's one that requires pre-school - but it's highly unlikely they're doing a lot of formal work. My first student teaching experience was in 2nd grade. I was surprised how much of it was classroom management and how little teaching - and that was 2nd grade! I ended up teaching middle and high school - at least I felt I got to teach a lot there.
If your child wants some formal work, then it is okay to do some of course. But don't look at the clock. Look at your child and what your child wants to do. Zero formal instruction is needed at that age. But if a child wants some, then of course give some. If you really want to count how long your schooling is taking, count more. Don't forget to count those books you read, those conversations you have that end up with some learning in them, even going to the grocery store is educational to a child that age. It's likely your child is learning many hours a day - even if it's just 30 minutes of what you're thinking of as education. Young kids learn so much through play and their experiences. If you're counting hours - you need to count that too.
I want to give him a true diploma, so he can say he graduated, so we have to go by our county grad requirements. But I like the idea of taking something like Astronomy for Science. 
