There’s a difference between productive and deep focus. Even if it’s a factoid, based on personal experience and anecdotal evidence from colleagues, 4h is a go

There’s a difference between productive and deep focus. Even if it’s a factoid, based on personal experience and anecdotal evidence from colleagues, 4h is a good approximation. I will admit though, that there’s a confounding variable here, that is how much your coworkers value your time. When I worked 4h or 6h workdays, everyone considered my time to carry a premium, so they avoided interrupting me if they could.