If you are using the equipment to play or to help achieve an erection, then simply use at will. Remember to shave the area where the vacuum seal will be made, lube up and begin pumping. Go slowly, create a nice comfortable suction and slowly increase the vacuum for the desired results. Increasing pressure too quickly can be painful and unless that is your goal, it's not necessary. If your goal is to enlarge the cock, balls or nipples then you will want to be on a schedule.
Different people get different results.
You will need to find the schedule that works the best for you. The important thing is consistency. Pick a schedule and stick to it. My experience in pumping men has been that more frequent sessions of a shorter duration are less likely to distort the shape of the penis. That's a rather relative statement.