I'd recommend the ground be swept first to remove rocks that might cause the golf to fly stray. Warn the students to be on their toes. I have watched youngsters launch bottle rockets at each other at New Year's and hence have some confidence that students can avoid being hit. Pick you ball pitchers well. No fancy equipment needed.
Friction introduces errors which permit an opportunity to discuss errors.
Hang them anywhere. Discretely knock a small finishing nail into the top of a door frame. Or use a sturdy light fixture. Or a beam. If these are not available just use any watch that has a smallest division of seconds and take measurements to the nearest second.