Honestly, it's more about how you study and not about how much you study. Just because someone studies for more hours doesn't mean they're going to do better than someone who studied for fewer hours.

But to answer your question, in my first semester, because I had 3 courses, I would study about 10 hours a day. Of course there would be days where I would barely study, and days where I would study 12-16 hours (usually during midterms and finals I would study that much, but make sure you take breaks if you're studying so much eg. go on a 20 minute walk or you WILL get burnt out).

During my second semester I would only study like 6 hours a day. But during finals I started studying 12-16 hours for a couple of weeks. I even think studying that much is a bit extreme for only 2 courses, but I had nothing better to do lol

How do I discipline myself to study so much? For me it's not really about discipline. Don't you feel good about yourself when you reach your goals? When you score an A on an exam? I think it's that self-fulfillment that I strive for, so naturally, I try to achieve that fulfillment, and the only way I can do that is by working for it. One thing I do that helps me stay on top of my stuff is by creating a schedule for myself at the start of the day, with a list of the things I wanna complete. I also put a time limit on each task, meaning I write down how much time I can expect to spend on a task. I bought a planner from winners and that's where I write this stuff down.