You know when you are driving a manual car or motorbike, there's that perfect friction zone where it just moves perfectly. Too little and it doesn't, too much and it stalls.

Work hours also have that friction zone. Too few and things take forever, too much and the project will stall (burnout, people leaving, human psychology, etc).

One hour in the "flow" for me is better than a week of work without that state of mind. When you are in the flow, things just get magically done, everything seems crisp clear and solutions to the most complex problems come off the tip of your mind as if it was nothing. You are effectively working at 10x speed and accuracy. Being exhausted or overworked makes sure you never reach that state AND introduce a lot of mistakes and inaccuracies those will stretch the project even further to debug and fix those.