list this word in one line so it doesn't seems like it should have lots of nuances.
Here some usage in my textbook. 出席 してこそ、授業の意味があるのです。
implies a sum of knowledge passed in class time.
Is 授業 really defined so broadly? What are the its limits of meaning and how to discrimate in practice? www.jisho.org lists 授業時間 as class-time, are there correct term for scheduled class-time and actual class-time? I know from my time as an ALT in a Japanese high-school, these are certainly not the same periods of time.