I can't say mine is as strict as they were - in late 80s, I went to school around 7am, and came home around 11p. Actual classes started at 8am, but pre-1st hour period was mandated. Regular classes, IIRC were over around 5pm, as it included 2 hour extra classes for everyone. I attended pretty competitive private school, and I was fortunate to be in top 10% of students. Those who were in that group, were separated to "superior" class - that were subject to do the study in school's library after school - the aim for those class was to put more students into named university & which meant the success of the school/
My school literally didn't have any extra-curriculum activities except select few that's part of academic success... and many didn't choose. I chose to be school's library club, just to have chance to relax with my peers and slack off. Since I was library club member (which as far as I can remember nobody took out any books to read for decades, as I could check who checked out the book, and many of the dates were from 70s) - most people who came to library were to study in quiet, air-conditioned environment where nobody made any sound.
Those "superior" class self-studies which happened promptly after regular classes around 5pm, with 1 hour break for cleaning & eating supper you brought home or school cafeteria that sold some light meals... then we were to go straight to the library and study till 10p. And being librarian, I was able to just sneak out from my seat and go into the club room and relax a bit, or do the study in that room separate from the rest of the students, who were basically packed in very small cubicles like caged chicken.... Sometimes I climbed to the roof of the building, and looked out - while my peers watched out for the teachers who came around unexpectedly to watch the students.
My younger brother, who was academically better than I was (He was #1 at everything) - he went even further. When he came back home, he studied until 1-2am, then went bed in his school uniform, wanting to get just a few more minutes of sleep.
I came to U.S. in 1990. Due to my reading being so much slower than natives, I had to spend about 6 times longer to really do regular home work... but even so, I thought U.S. public school was easier. High school math was easiest as I already learned trig and calculus at 9th grade - so solving any math equations were easy. What got me was though - to comprehend the question itself, and also doing written out explanation & proving them. Same went for the science too.
But even so - my generation - gen X - didn't have to deal with these types of extreme environment post education like they are facing in Asia. These days, I see young Asians giving up many things - love, marriage, having children, buying homes, getting stable employment.... and these gaokao types of hyper-competition, is one of the root of the people giving up. Success in China isn't like before - where people came in from rural area to the city, worked their bones off and saved, became successful... these days, unless you have good guan-xi, and best education at top universities and financial support from family, it's extremely difficult to get ahead, or even settle down and create a family.
Herbivore men or Satori generation in Japan, N-po generation in S. Korea, and most recently Tang-ping movement in mainland China - and I honestly don't blame them for what has happened.
China's population has gone down and their recent 3 child allowance policy were met with such cynicism, as well as they entered aging society well before their gdp per person has entered developed country level. Japan is oldest country that many cities are becoming ghost towns. S. Korea's birth rate is like 0.8, and lowest in the world (except those small city-countries), and they will be gone in a few hundred years if this continues. S. Korean government spent like 150 billion dollars to encourage people to have more children, but young people are just giving up and birthrate is plunging down. I won't be surprised if it hits 0.7 next year.
To be honest, I don't know how it will be like in just 10 years from now. Whenever I visit Japan once in a while, I'm always pretty shocked how stale the society has become. Everything has been kept up so clean, but all of them, system and all are so old - as if they are stuck in 80s-90s... and while I enjoy my nostalgia there - but also at the same time I feel rather sad of seeing a dying country. Korea, is more dynamic in appearance, where everything is super new and fancy - but with this type of birthrate and all - how long can they keep up with it when young people are dropping out and giving up, and there are literally less and less children being born..? China is actively trying to shame the young and quickly shut that tang ping movement.... but I am not sure if they can contain.