Depends on what stage the students are at.
I liked when they got to the point that every class was about 1 hour learning and practicing applications with a partner, and 2-3 hours of medium contact continuous sparring.
The students would spar until they were too tired to continue, then it would be the next guys' turn. I would spar 3 in a row then break. I also coached during the sparring to correct mistakes and point out how to capitalize on things they could do well.