I have found over the decades that my debugging ability declines as fatigue increases. So if the goal is working code, there is a point where the additional work leads to delay whenever something is broken or has to be changes. Hack attacks of short duration is great to get some code off the ground, but anything that must be maintained must be clear enough to be revisited later. I have tried to average 45-50 hours/wk max, although sometimes out-of-work swaps for in-work time.