Everyone's code breaks eventually. Even the people who spend 8, 10, or 12 hours in the chair. The solution is not to require that everyone spend 8 hours at work

Everyone's code breaks eventually. Even the people who spend 8, 10, or 12 hours in the chair. The solution is not to require that everyone spend 8 hours at work. Rather, it's to require that the code be explained and discussed in code review. After that, there's an on-call team (which may or may not include the original developers of the code!) who handles the system in case of a breakage. Butt in the chair time is completely irrelevant to this process.