As the husband of a public school teacher, I can tell you that that if you were to account for the total hours spent dedicated to work beyond her contractual obligation to be at the building, it stretches significantly beyond 180 days. I couldn't begin to give you an estimate of how much more, but grading, lesson planning, prepping materials, conferences, it adds up.
I've spent plenty of Saturdays with her at the building making copies, laminating, hole punching, etc to make sure we can get on with our weekend at a reasonable time.