How much time should be allocated to supervising undergraduate researchers?

I recently asked this question about how many office hours per week are common for undergraduate lecturers but then I just read this one about supervising research done by undergrads. This got me thinking that perhaps my previous question was going in the wrong direction.

I have >300 students in 3 different subjects. 200 of those students are in one subject and that subject requires students to do extensive research. My challenge (explained in the question linked above) is that I seem to have too little time to properly support this many students.

These are business students so there is no lab. The research is reading the literature, finding data, integrating the two into some meaningful insight.

So, my question is, when supervising undergraduate students who are doing research, how much time on average, per week, per student, should this consume of the supervisor's time? 15 minutes? 30 minutes? 1 hour?

Edit: To put this in perspective, the students are not writing a bachelor thesis. However, they are expected to put in about 100 hours of non-class time (after the class time has finished) doing their research and writing it up. The final product is about 4,000 - 5,00 words (so far less than a thesis).