If I have a 45 minute rehearsal where I've talked more than 5 minutes, I'm extremely disappointed in myself. BTW, Today I was disappointed in myself lol. But, my point is that students want to be in band to play their instruments. Your lessons (rehearsals) must be organized to where you're leading them to knowledge and (quite a bit of) self exploration in their playing. If you're telling them everything without them problem solving you're doing it wrong. Took years for me to learn this. Most of my comments are very general during a rehearsal. "Careful clarinets in m. 5, somebody isn't using the key signature there." Usually comments like these fix most things and make the kids not afraid of you and cause a nicer rehearsal environment. Every now and then you have to really talk something out. Now, I was told by a great mentor early in my career that if you find yourself talking a ton during class the problem could be with the music you have picked out. Growth in band programs is very gradual. So I would say that the 5 minute rule is a great one. Small, meaningful comments that are to the point and don't break the flow of the rehearsal are important. They'll appreciate a rehearsal like this. I'm going to do this better on Monday with my high school band!! =)