The average school day in the U.S. is ~6.5 hours according to https://nces.ed.gov/surveys/sass/tables/sass0708_035_s1s.asp https://nces.ed.gov/surveys/sass/tabl

The average school day in the U.S. is ~6.5 hours according to https://nces.ed.gov/surveys/sass/tables/sass0708_035_s1s.asp https://nces.ed.gov/surveys/sass/tables/sass0708_035_s1s.asp The article suggests most subjects are taught using online courses. And because they all take math and english (the only non-online classes) in the first part of the day, I think there's the implication of a relatively small number of students, perhaps comprising only one or two classes. So compressing 6.5 hours into 5 hours that way doesn't seem unreasonable. Though that still leaves the question of the efficacy of online instruction.