I don't believe the study everything, prove everything you do level is attainable with 5 hours per week for 3 years at the high-school level, even with a very good self-selected student group.

The German school system starts by separating students into 3 different kind of schools based on the academic skill of the student: Hauptschule, Realschule and Gymnasium. The Gymnasium is basically for those who go to university. That separation starts by school year 5 or 7 depending on where in Germany the school is located.

You have more than 3 years of math classes at school. I think proving stuff started at the 8 or 9 school year. At the beginning a lot of it focused on geometry.

At the time I think it was 4 hours of math per week for everyone. I think there were many cases where the students who were good at math had time to prove things while the more math adverse students took more time with the basic math problems.