Answer:
Yes, I agree with Powderly's stance on the eight hour workday. As it is very difficult for an average man to work for more than 10 hours a day even an average brain and body can take up to 6-7 hours of work pressure.
What the labour was doing was extra work. It is ideal for a man to work for 8 hours and then take a rest to regain the lost energy so as to perform better the next day.