The best guess I have is sometime around the beginning of 1993, when Clinton took over the presidency. Was it then that, just to take one example, Donna Shalala moved from the University of Wisconsin Madison to Secretary of Health and Human Services-- typifying the movement of political correctness from university campuses to mainstream politics? (And perhaps it should also be noted just which Clinton should be attributed the real credit for such appointments?)
Sorry, but you're at least 2 or 3 decades late in your estimation of the beginning of the era of PC.
As gratifying as it might be to some to blame everything bad happening in western civilization on the Clintons, PC didn't start on their watch. It seems much more likely that they are the ultimate product of political correctness, as the tide seems to be receding for PC.