Well it does depend. My oldest spent less time In 9th grade. There was a transition and lots going on outside of school. By Jan, my kid realized it was going to take a ceratin amount of work to get top grades. Like another poster above, little time was spent on math ( an easy subject) and more was spent on other subjects.
My kids have found that the amount of work required to get a solid grade is 2-3 hours a night. But to be in the top tier of students in advanced/honors/AP classes takes a lot more.
I don’t think an AO could tell you. It depends on your kid, their focus, the grades they are comfortable getting and their facility in each subject. Your kid might have a subject or two where very little work is required. But the norm is most kids are working in every class.
There are also some teachers who are very difficult. Can be in any subject. These teachers require more than a normal amount of work. Often it’s luck/random. One group of kids gets one teacher and the other group gets the difficult teacher. You can’t switch back and forth. My oldest got a difficult science teacher but got the easier Calc teacher. And subject doesn’t always matter. Chinese might be easier than photography.