How much time elapsed between Noah and Abraham, and where does the Tower of Babel fit in?
Roughly 400 years elapsed between Noah and Abraham. The Tower of Babel fits in the middle of that interval. By Abraham's time, about a couple hundred years after Babel, the known world was steeped in idolatry. At Babel, humanity still had one language and gathered in the plains of Shinar.
Les teaches that the interval between Noah and Abraham is about 400 years, roughly speaking. In the middle of that 400-year period stands the Tower of Babel. He explains that after a couple hundred years from Noah's three sons, the human race had not yet multiplied into millions but was already quite a few; they were still of one language and one blood. They all met in the plains of Shinar, in Mesopotamia in the Euphrates River Valley, and built the Tower of Babel. Les stresses that at that Tower, under Nimrod, Satan—the god of this world—instituted all pagan and mythological religions, so every pagan or idolatrous religion began there. By Abraham's time, a couple hundred years after Babel, at 2000 B.C., the whole then-known human race was steeped in idolatry or mythology, such as the Venuses and Aphrodites. Out of that race saturated in idolatry and paganism, God found one man who still had a spark of faith or the ability to believe.