4 Pass 5 Fail

While studying in my school I've learned alot about the japanese culture.
There's 1 idiom that's playing in the heads of me and my classmates.
It's 4 Pass 5 Fail (四当五落). What it means is if you sleep 4 hours a day you will pass your exams but if you sleep 5 hours den you're sure to fail.
My assistant headmaster always ask us how many hours you studied yesterday ?
I'll be hiding my face cause I dun study after school.
The advice he always give us is you gotta study at least 5 hours a day after school.
Sleeping too much is useless. So he's giving us a discount.
So in conclusion we should only sleep for 6 hours a day and must study 5 hours a day.
10 hours for the weekends. He's trying to kill all of us.
This is some kind of japanese extremist idea of studying. This is driving me nuts.