I started secondary (grammar) school in 1968, and still have my original timetable from my first year. it comprised of 7X40 minute lessons per day. Over the course of a week, my lessons were as follows:
7 Mathematics
7 English Language
3 English Lit
3 French
3 P.E. (Games)
2 History
2 Geography
2 Biology
2 Chemistry
2 Physics
2 R.E. (Religious Education)
I seem to remember that for the second year, certain subjects (such as German, Latin, Commerce etc) were introduced, and you had the choice to drop some of the "lesser" subjects if you wished. If memory serves, though, we still had to take the "full quota" regarding Maths and English.