[hmbg]

It might be correct about the 4 hours. It might also be irrelevant for most people. For most disciplines, accomplishing anything consists of some cognitively very demanding work, and a lot of 'admin'. Some violin players and mathematicians may get by on doing only the hard stuff, but most have to apply for grants, participate in conferences, transcribe/arrange, maintain equipment, etc.

For a startup founder I think this is especially true. A lot of the things you do won't be very cognitively demanding. That doesn't mean you can skip it if you want to get anywhere. It doesn't even mean those 'menial' task create less value in your context than the hardcore 100% concentration parts.

Maybe when you've settled down to a predictable working pattern and managed to configure your environment to cater to all the necessary but trivial tasks (and create enough value in your 4 hours to pay for other people taking care of the rest) you can realize this. I'm not there yet.