How u know he doesnt practice full time?? These victories certainly are the result of hard trainings .
I'm going to warn you in advance. It's going to be a long post.
How do I know? Well, I've been involved with U12 scene in Japan for 10 years due to my daughter's involvement as a competitive junior player. There are lots of people who know better but I think I know more than the most.
First of all, I don't believe in practicing long hours. Training hard with good coaches and partners is necessary and you'd choose quality over quantity if you had to make a choice. Having said that, putting certain numbers of practice hours is a must for top players as coaches in this forum would agree.
Before I get into Harimoto's practice routine, let me explain the current U12 scene in Japan.
In Japan, the National tournament is held every year for U12/U10/U8 categories. Top players in U12 are then recruited by private school and Elite Academy. 99% of current top players have performed well in these tournaments (notable exception is Oshima). The importance of practicing long hard hours from very young age have been recognized ever since Ai Fukuhara's practice with her mum was televised 25 years ago. According to the survey conducted at U12 national tournament a few years ago, more than half of the participants practice more than 20 hours per week, 20% have put in 30+ hours and few have even clocked 40+. And that's with either your parents or hired coach from China (eg. Matsudaira, Hirano, Ito).
My daughter's club didn't have that luxury, just like most other junior clubs in Japan. Sure she practiced 4 hours in a week day and 6 hours in the weekend but she was always beaten by kids that were privately coached or had parents who owned junior club themselves.
So when Harimoto won U8 tournament aged 7 (back then he was Zhang with Chinese nationality), we were like "Right, another kid with Chinese parents who devoted their life to their kids". But the fact was quite different as we got to know about them more and more by talking to them occasionally or hearing about them when we see them at the tournaments.
It turns out, he was closer to "us" than "them" in terms of environment. His parents were hired by Sendai junior club as a full time coach so they didn't have time to teach Harimoto privately except for their off days when they spend about an hour with him. We didn't believe them at first. How could a boy so exceptionally good and absolutely dominates his age group only practice 2 hours a day and even that's with other members of his club so he has to pick the balls and share the table just like everyone else. Well, they weren't lying and by the time he won the national tournament 6 years in a row in 2015(beating a boy from my club on the way), no one was sure of how far he would go when he starts devoting all his time to table tennis. That year, he was already beating U18 national champion as well as some top senior player in Japan.
That almost happened in 2016 when he had to make a choice after graduating primary school. In the end he chose the Elite Academy which was and still is funded by JOC and other governing bodies. Because it's state funded, minimum academic standard must be met and you need to attend unrelated course and seminar such as media presentation organized by the Elite Academy. It means that typical week day only allows 2-3 hours of practice. This is a stark contrast from top private schools in Japan where scouted players finish school on 2pm and practice 6 to 8 hours per day. It was no surprise that until Harimoto and Hirano, there were hardly any top players produced by the Elite Academy. Players like Hirano and Miu Kato probably made a right choice by leaving the Academy before the age limit of 18.
So, back to my original statement. I'm looking forward to the day he graduates Elite Academy and devotes all his time playing table tennis. He has already achieved more than most players on this planet even if he retires today. I somehow feel there's lot more to come.