[watwut]

Based on pretty much everything I have seen and read, no one can work 12h every day, 7 days a week and deliver quality. Simple, such person does not exist. People can spend a lot time in work doing all kind of adjacent stuff - staring into wall during long meetings, talking with colleges, staring into screen, etc etc. Too much overtime also leads to a lot of fixing of mistakes that did not had to be. No socialization outside of work invariably means a lot of unnecessary long meetings, because people need to talk and this is their chance.

However, if 4h limit really exists, imo, it will be about focused hard stuff. Many many programming tasks are not difficult and you can safely easily do them longer. You can also mix programming with analysis, architecture, design, helping people etc etc easily being able to productively occupy yourself for more.