When did Noah start building the ark according to Hebrews 11?
According to Hebrews 11, Noah began building the ark only after God spoke and commanded him to build it. He did not jump the gun or start on his own initiative. By faith, he responded to what God told him to do, and then he built the ark.
Les explains that Noah did not jump the gun; he did not start until God said, "Build an ark." Hebrews 11 then says that by faith Noah responded to what God told him to do, and he built an ark. Les compares this to Abraham, who left Ur of the Chaldees only when God said to. The pattern is that when God speaks and men respond, God sees it as faith and reckons that faith. Les applies this same principle to the Gospel: God has now revealed it through the Apostle Paul to the Gentile world, and Gentiles are responsible to believe that Gospel.
By faith Noah, being warned of God of things not seen as yet, moved with fear, prepared an ark to the saving of his house; by the which he condemned the world, and became heir of the righteousness which is by faith.