That seems as much of a watershed moment as any, and I’d have to hand it to the Reagan election if I had to pick a moment and restrict it to the political realm. Reagan seemed to be the one skewing us toward post-truth politics. Nixon cared about the truth in the breach, whereas Reagan just said anything regardless of its truth value: of course, not compared to some others one could mention.
I was 20 in 72. The watershed year was 1968. After that Vietnam was widely considered a lost cause/bad idea. The next 15 years were were all focused on adjusting to new realities. We all knew race relations, politics, economics, foreign policy etc were going to change. Some looked forward to that others did not. But everyone knew change was happening. Depending on your station in life change was an improvement or not. 1972 was just another year of change. Lots of change, but no more than the year before or the years after.
As for a “post-modern” era, I think it consists of the acceptance and embrace of change that best marks this era. That didn’t happen until the 80-90s. It wasn’t until change, newer better cars, computers, cheap airfare, integrated circuits, etc brought benefits to everyone that people starting viewing change as something good. Before, it was never really viewed as good. Sometimes necessary, for instance race relations, but never something one looked forward to. Growing up, it wasn’t until the 80’s or so that I even started looking forward to new and improved products. Certainly improved has been trumpeted as good since advertising was invented, but that idea was always viewed as advertising. This year’s car was different from last year, but not considered better except that cars only lasted 2-3 years and a new car had 2 years of life in it. By the late 80’s, due mostly to personal computers, change was recognized and valued in many areas of life.