I mean you can visit Tokyo and barely notice anyone being fat while in New York there’s about 30% people being obese, even though both countries have fast food. Although Japan has less of it tending to burn off that by walking or exercise (it also reflects their lifestyle) and portion sizes regarding food & calorie intake while in US there are literally multiple fast food joints next to each other along with huge portion sizes.
I read a lot of manga, and the amount of references I see to going to school on a Saturday or leaving the school building at 7pm. It is unreal to think about.
Leaving later can be because of 部活 which is often translated as ‘clubs’ but I might call them extracurricular activities coming from the US. Dance, table tennis, soccer, baseball, chess, electronics, swimming, etc.
Growing up in the US, I did band, theater, sports, etc. and it wasn’t uncommon to be leaving school fairly late because of it (theater especially).