How long had Abram been waiting for God's promise to be fulfilled?
Abram had already been waiting 36 years for the promise of Genesis 12 to be fulfilled. That promise was that he would have a son, and out of that son would come a special race or nation of people. This waiting occurred as years rolled by chronologically, with no child yet born.
Les explains that this passage is within a chapter or two of the Abrahamic Covenant, but years have rolled by chronologically. Abram, still known as Abram there, had already been waiting 36 years for the promise of Genesis 12 to be fulfilled. That promise was that he would have a son, and out of that son would come a special race or nation of people. Les notes that 36 years is a long time in any period of human history, and there was still no child. He urges not to get too impatient with Abram, since we might feel God had forgotten and was never giving him the promise. Sarai had no signs whatsoever of ever being able to have a child.