I'll give you that not everyone is productive at 12 hours - but I'm not talking about everyone or even averages. The point is there are plenty of counterexamples of people that can work 12 hours days for months and are way more productive than anyone working 8 (hence "rock stars"). Some people really really love programming and don't have a life outside of work. A simple example is the overzealous founder/cofounder programmer that works 12 hours a day. I've seen people do that and they are very very productive b/c their heart is in it. I imagine some people with lots of stock options and/or coolaid-drinking also are very productive. Some people I've met that work at SpaceX sound incredibly productive. They probably eventually burn out, but with turn over being so high in our industry as it is, your employer doesn't really care. You'll leave after a year or two anyways.

.. The link you put up is full of conjectures, but I didn't actually see any numbers... (it's a link to class? .. I don't even understand the website)

I'm thinking more in the vein of

https://en.wikipedia.org/wiki/Brooks%E2%80%99_law

"adding manpower to a late software project makes it later"