When did God first give written commands about what men could and could not do?
God first gave written commands about what men could and could not do at Exodus chapter 20, when Israel was gathered around Mount Sinai. From Genesis 1 until Exodus 20, there had been no written do's and don'ts from God, so Sinai marks the beginning.
Les teaches that from Genesis 1 until Exodus 20 there was never any written do's and don'ts from God concerning what men could and could not do. He also notes there had not been one single item of God-instituted worship until that point. After the 430 years were completed, the nation of Israel was gathered around Mount Sinai, and God was getting ready to do something totally different than He had ever done before. That is when the written commands began, at Exodus 20.