They were comparing against kids in Australia. I forgot the exact details, but the policy developed was to add additional time during schools, and educating parents. Two hours a day cumulative, five day a week or something along those lines.

This isn’t something one has to spend a lot of time optimizing within certain latitudes, since there are benefits for kids being outdoors beyond halting progression of myopia. Although, if you think this can reverse myopia, it is worth biohacking.

If I recall, the article I read on this was posted on HN.