I usually do a minute at each station. I find its easier for me to keep track and the participants as well. To make it flow easier, I show the exercise, a modification and a progression for each exercise. Then those who want more of a challenge can do so. Those who are just starting out, don’t feel singled out. I also let them know to try to get through the entire minute. If they need to drop to a modification, that’s ok, the goal is to just keep moving using good form and executing the exercise properly. If at any time form is compromised, they are to stop and march it out.