1972 Unix V2 "Beta" Resurrected

I once saw a talk from Brian Kernighan who made a joke about how in three weeks Ken Thompson wrote a text editor, the B compiler, and the skeleton for managing input/output files, which turned out to be UNIX. The joke was that nowadays we're a bit less efficient :-D

I’m wondering what the process was for the early UNIX developers to attain this level of productivity.

Did they treat this as a 9-5 effort, or did they go into a “goblin mode” just to get it done while neglecting other aspects of their lives?

Back in my early career, the company I worked for needed an inventory system tailored to their unique process flow. Such system was already in development and was scheduled to launch "soon". A few months went by and I got fed up with the toil. Sat down one weekend and implemented the whole thing in Django. I'm no genius and I managed to have a solution that my team used for a few years until the company had theirs launched. In a weekend. Amazing what you can do when you want to Get Shit Done!