thoughtbot works 9-5, Monday-Friday.
Energy is finite. Anyone working 12 hour days will not be doing their best work a few days in and will crash at some point.
Extreme Programming advocates call this “Sustainable Pace.” Other than keeping everyone fresh, it makes planning more predictable as the past becomes more indicative of future performance.
Startup lore is filled with glorious stories of late nights eating Ramen and coding out those features that will make millions. Reality is that the best features were probably created during bank hours.