The idea is a challenge. Why would God allow any other human to suffice for what the Father gave His only begotten Son to accomplish? That came centuries later. Meanwhile, had Abraham succeeded in sacrificing Isaac, wouldn't God have had to honor that as sufficient for all? God would not allow that then or any other point in time until Jesus could be prepared for that role of substitution. What Abraham was willing to do set up a continual hope that God would be known to supply the perfect Lamb for us all. Notice the boy was not Ishmael, born out of the covenant of promise by the womb of Sarah.I'm not sure I understand what you are asking. What are you calling a 'delayed Jesus offering'? Are you saying Christ's offering on the cross was delayed? Are you asking why didn't Christ come immediately after Adam sinned?