Blood flow rate help

Hi. I’m new as a dialysis nurse. If the treatment nearly ends, How many minutes are left before we lower a patient’s blood pump? I’ve seen some colleagues lower the blood pump from 300 to 180 20 minutes before the dialysis ends, and some lower it by 10 minutes, but as for me, I lower it when 5 minutes are left. I lower the pump to 250 first then after two minutes before it ends I lower it to 180. Please correct me if I’m doing it the wrong way.