Maybe European schools are really different or maybe I'm studying effectively but I've found that I only need 1-3 hours a day if I just wanna keep with the pace and I skip lectures. However, on most days, I study 6-8 hours just so I can stay ahead by a lot or because I've simply not studied for a very long time.
It is also a matter of being able to filter the information. Do I really need to know every enzyme name in some pathway and the structure of each involved substance or only learn the names of the intermediates and some important enzyme names and their means of regulation? (currently we're on biochemistry)
Study method may also change the way you study by a lot. So as I said we have biochemistry. I just make a bunch of flashcards. With Anki, I'll remember this shit two years down the line when we have our equivalent of Step 1. I know a guy who used Anki for two years and before our Step 1 he didn't use his dedicated two weeks to do any real studying, he remembered it all already. He got the highest score in class and he was one of the people who studied the least. The initial time investment is large when making the cards but making the cards you also remember a lot. The maintenance investment is pretty low.
For example, I have 4000 cards now with only a month or so left of my first semester and I only do 150-250 cards a day that only takes half a hour or sometimes even less. On days where I don't feel like studying I can at least rest well knowing that I'm not forgetting anything. I have friends who dedicate whole days to review old material and or failing tests that test old content. I'm passing with great scores and I can solely focus on new content. Sometimes I do need a concept refresh as Anki should exclusively be used for details (note however that repetition of details automatically refresh concepts most of the time, especially if you have nice concept pictures with some cards) but I usually just watch a video by Kaplan.
So as said, it depends on your study techniques. I'm also lucky that we have access to our old exams and that teachers like to reuse them so I made each and every question on past exams a flashcard (making sure to break up large questions into several cards) and that takes down my studying time by a lot.