I find the biggest asset to learning a concept is being to rebuild it if you are presented with a slightly tweaked problem or you flat out forget a formula.
Most of my college exams were 3 hours, but those who were adequately prepared could usually finish between 30 mins and an hour. The other 2 hours were generally for trying to scrape your brain for any clue as how to pass the test.
And college profs love to give tests with only a few questions. I had so many 3-5 question tests where each question was literal pages of work. And each question was a unique concept which required a synthesis of concepts we had learned throughout the semester.
I was a poor student. On several occasions, I flat out forgot the relevant equations and had to re-derive them on my own. It’s what got me through classes like diff eq and thermodynamics. Eventually I grew up and started taking college more seriously and studied more than just the night before.