Since when has the whole human race been saturated with idolatry according to Les?
The human race has been saturated with idolatry of one sort or another beginning at the tower of Babel. From that point onward, idolatry spread across the whole human race in various forms. This is the historical starting point given for humanity's widespread false worship.
Les explains that he regularly reminds his classes that beginning at the tower of Babel, the whole human race has been saturated with idolatry of one sort or another. In the surrounding context, Daniel is brought before Nebuchadnezzar and testifies that there is a God the king knew nothing of, in contrast to the wise men, astrologers, magicians, and soothsayers. The passage presents the almighty sovereign God at work, revealing the secret to Daniel, while humanity since Babel has been marked by idolatry in some form.