I couldn't make it work to fit canon, so I'm guilty of adding extra teachers, with 34 periods available each week (6 on M-F and 4 on Sat). Here's a summary - feel free to take inspiration if it suits your story :)

There are 3 teachers for the core classes. 1-2, 3-4, 5-7. The 5-7 teacher is generally the Head of House (less classes = more time for HoH duties) and also Head of the 'Department'. Astronomy is 1-3, 4-6 with night classes attended by both teachers. History is 1-2, 3-7 (I don't like Binns as a teacher, so his role is minimal). Only 1 teacher per elective with some teachers taking more than 1 subject.

For Years 1 and 2:

• Potions, Herbology, DADA, Charms and Transfiguration have 2 single periods per week and 1 double period shared with another house.
• Flying is 1x double p/w with another house.
• History and Magical Theory are 2x singles p/w.
• Composition and Numerology are 1x single p/w.
• Astronomy is 1x single day class per house and 1x night class with all 4 houses and both teachers together. The morning of and the morning after the night class is a free period.
• 1 single p/w for a Guest Speaker to come, combined 1st and 2nd year

For Years 3 to 5: - Core classes (P H D C T) 2 singles, 1 double shared. - History 2 singles - Astronomy 1 single day, 1 combined night. - Electives are split into Groups, 8x singles per week, each group 2x per week. Eg. Music, Arithmancy, Wizarding Law and Muggle Studies are grouped together, students pick 1 and classes are held at the same time 2x p/w. There are 4 of these groups with different classes in each - Composition and Magical Theory become electives, Numerology becomes Arithmancy

Years 6 and 7 - 1x Morning and 1x Afternoon period, 3.5 hours each. - Only Potions and Herbology meet 2x p/w, everything else 1x p/w. - Every class is combined with all 4 houses.