I can relate how long I spend, in my own experience. My experience is in mathematics and computer science, which may be different from other fields.
When I wrote my PhD, I usually met with my advisor for about 1-2 hours each week, unless there was a special reason to have a second meeting.
I work at a department with a master's program. When supervising a master's thesis, I expect to meet with my advisee for about the same amount of time, about 1-2 hours a week, unless there is a reason to meet a second time.
Similarly, when I co-authored a paper with a strong undergraduate student last year, we met for about 2 hours a week for a semester and a half. Part of this was instruction by me about the area, and part of it was research meetings to engage with our problem.
When I advise an undergraduate "senior project", I set up a meeting for one hour per week with each student I advise. These projects are "research light" at my institution, and can even be expository for some students. But at least one senior projects I have supervised developed into a different co-authored paper, so some real research is done as well.
In every case, I expect the student to work for several hours between each of our meetings. When they are writing, I require them to send a draft at least s day before we meet, so I can review it. When they are writing computer code, I also require them to send that a day before we meet as well. This helps me keep the meetings productive - we can talk about challenges they have encountered in the research, or about my feedback on their work, or about future plans, etc., with a minimal amount of wasted time during the meetings.
Each time I have a meeting with a student, I try to make a plan before it begins about what we will talk about. Of course, if the student has something more pressing to discuss, that takes precedence over my plans. But I try not to waste and meeting, because that leads to having to meet again that week or to slipping deadlines, both of which I want to avoid if possible.
Of course, you cannot possibly meet for one hour each week with 200 students. I find the even four personal meetings per week is more than enough to keep me occupied - both in terms of time and in terms of mental capacity. So you will need to find a way to economize, and give less personal attention. You might try organizing group peer review sessions.
Frankly, I am surprised you can even grade the 200 papers that are written - if you can manage 30 minutes per paper all day long that is still over 2 weeks of grading!
If you have any say at the department, you might propose having the students work in groups; 50 groups of 4 is much more appealing than 200 groups of 1, both for advising and for grading.