When I worked at Microsoft, Windows took far, far longer than an hour to build from scratch. I remember walking a few buildings over to the burn lab to pick up DVDs of the latest build. I don’t have any hard data, but running a full build on your dev box was very rarely done.

The dynamics of commercial projects can be very different from open-source. You're much more likely to tolerate sitting through long builds if you're being paid to do so.

Until management notices, does the X hours saved multiplication by number of developers, and the resources for improvement will be found soon.

Definitely not. People are far more expensive than machines.

Was it just the windows kernel? Or did it include all of the utilities in Windows?