Use the zoom lens occasionally. Record each group. You'll find the plays can be performed quickly, in about 5 minutes. Since most camcorders can be attached directly to TVs for playback, it's usually no trouble to show the class their performances. I usually do so the next time the class meets.
Time management is critical.
This time allotment is for a class of 40 students. Smaller classes would ta ke less time. In this case, you can spend more time on practice and rehearsal. Make sure the climax of the play is emphasized. Encourage students to be dramatic at this scene.