If you don’t have the option of electronic timing then you can always do it based off of feel. It’s not precise science but that’s what my old coach would do and if we were supposed to hit 8×30 and on the 7th I felt a little tired he would ask for feedback and then we might scratch one. The same could also be said if an athlete does something really fast. You could possibly cut the workout short and decide that they are ready and don’t need the extra volume since the effort might not be as good as some of the previous. I think this is where the art coaching comes in and deciding what the athletes needs and doesn’t need. I am entering this convo late so I apologize if I missed some things.