How old were the ones you dated?

In general, the hours spent teaching diminish over time. At the beginning of a teacher's career, they spend a lot of time outside of class building lesson plans and creating tests and homework assignments. These legitimately take a lot of time. And they aren't perfect, so the teacher often sees that they need to make big changes after those lesson plans and tests and homework assignments hit the students.

But after a few iterations, they have those tools, and at that point things settle down a lot. The material only needs to be updated infrequently. Most of that time that in the first few years was spent building those things is freed back up, and it's not replaced by anything.