And so I was trying to get a handle on the size of the challenge, while I was writing this talk, and I found this newspaper clipping.
"More than 300,000 Americans, working for 20,000 corporations all over the nation, took part in the $23.9 billion effort. Just one key decision alone - settling on the method of going to the moon - required more than a million man-hours of technical study."
So I took a guess, at that talk, that the Moon landing was on the order of a hundred million hours.
Matt Webb, Web Directions South 2014 (Sydney, Australia), October 2014