Elite bodybuilders, lifters and athletes can tolerate and even prosper on explosive training because they have the required robustness of joints and connective tissue. But even they often pay a heavy price in terms of injuries, eventually. There is absolutely no need to take any risk with explosive training. A slower and controlled rep tempo is so much safer, and by far the best option for typical trainees. Why seriously risk pushing your body beyond its structural limits, and possibly suffering permanent injuries, when there is a safer way to train that is super productive?
Rather than try to find the ideal rep speed, focus on keeping each rep smooth, and totally free of explosive or sudden movements. In practice, however, smooth reps take about 3 seconds for each negative phase, and 2–3 seconds for each positive phase—and perhaps even longer for the positive phase at the end of a set when the reps grind to a near halt. Long stroke exercises require more time than short stroke ones.