Which country has the shortest school day?

There is no single official answer because school schedules vary by age, region, and how countries count instructional time. However, according to international comparisons of average school-day length, Brazil is often listed as having the shortest average school day, at about 4 hours per day. (World Population Review)

Some sources also identify Germany as having one of the shortest school days, averaging around 4.5–5.5 hours, depending on the state and grade level. (SpainExchange Country Guide)

Finland is frequently mentioned because many younger students spend only 4–5 hours a day in school, yet the country achieves strong educational outcomes. (Save Our Schools March)

Summary

So, if we look at international averages, Brazil is generally reported as having the shortest school day, while Finland and Germany are also among the countries with relatively short school hours. (World Population Review)