Our homeroom was like 10-15 minutes. It's where we heard the daily announcements, our attendance was taken, and sometimes we'd get info on things our class was doing. It worked out especially well for me senior year, as my homeroom teacher was also the yearbook staff advisor, and we would always get some yearbook-related work done before and during homeroom.
Though there are exceptions, in a lot of the high school anime I've seen, homeroom is the ONLY class that's shown. After-school clubs and lunchtime are shown as well, but many don't explore the other classes, or if they do, then only briefly.