High School: basically never, just usually paid attention in class. Did homework in study hall or copied somebody else's.
Undergrad: Mostly cramming before tests. Actually did my homework. For classes I liked, I studied a bit more since it was enjoyable. Imagine 2-5 hours a week outside of class.
Med School: Pre clinicals was mostly cramming for 12-20 hours prior to tests. However, the way the curriculum was set up, I had to do little presentations/small groups that reinforced relevant information. So I was kind of "studying" more often.
Clincal years: in free time at hospital, learning from residents/attendings. Didnt really do a ton of "book studying" except for a day before shelf exams. Lots of reading about patients/conditions during workday, but not too much at home.
Agree with other posters who said this approach doesnt work great for big standardized tests. I didnt study for the ACT in high school, but was able to get my **** together for MCAT and STEPs by studying for 3-5 weeks hardcore.
Everyone is different, just make sure you do enough to succeed. I was just above average for med school class rank, would've required way more effort to be at the top, which I was fine with.