After His baptism, but not because of His baptism. If you are looking to pin-point the event that afforded Him the reason that all authority would be His it would be the cross and the resurrection which was after His baptism. Here is the reason why I say this.
Luke 4:5-8 “And the devil took him up and showed him all the kingdoms of the world in a moment of time,6 and said to him, “To you I will give all this authority and their glory, for it has been delivered to me, and I give it to whom I will.7 If you, then, will worship me, it will all be yours.”8 And Jesus answered him, “It is written,“‘You shall worship the Lord your God, and him only shall you serve.’”
It was originally given to Adam and Eve in Genesis 1:28, they had dominion or authority over all the earth.
“And God blessed them. And God said to them, “Be fruitful and multiply and fill the earth and subdue it, and have dominion over the fish of the sea and over the birds of the heavens and over every living thing that moves on the earth.”
Jesus disarmed them on the cross taking away the legal demands of the Law, death for sin and He triumphed over them.
Colossians 2:13-15 “And you, who were dead in your trespasses and the uncircumcision of your flesh, God made alive together with him, having forgiven us all our trespasses,14 by canceling the record of debt that stood against us with its legal demands. This he set aside, nailing it to the cross.15 He disarmed the rulers and authorities and put them to open shame, by triumphing over them in him.”
Jesus died, rose again to life forever and now has the keys to Death and Hades.
Revelation 1:17-18 “When I saw him, I fell at his feet as though dead. But he laid his right hand on me, saying, “Fear not, I am the first and the last,18 and the living one. I died, and behold I am alive forevermore, and I have the keys of Death and Hades.”
Matthew 28:18 “And Jesus came and said to them, “All authority in heaven and on earth has been given to me.”
Luke 4:5-8 “And the devil took him up and showed him all the kingdoms of the world in a moment of time,6 and said to him, “To you I will give all this authority and their glory, for it has been delivered to me, and I give it to whom I will.7 If you, then, will worship me, it will all be yours.”8 And Jesus answered him, “It is written,“‘You shall worship the Lord your God, and him only shall you serve.’”
It was originally given to Adam and Eve in Genesis 1:28, they had dominion or authority over all the earth.
“And God blessed them. And God said to them, “Be fruitful and multiply and fill the earth and subdue it, and have dominion over the fish of the sea and over the birds of the heavens and over every living thing that moves on the earth.”
Jesus disarmed them on the cross taking away the legal demands of the Law, death for sin and He triumphed over them.
Colossians 2:13-15 “And you, who were dead in your trespasses and the uncircumcision of your flesh, God made alive together with him, having forgiven us all our trespasses,14 by canceling the record of debt that stood against us with its legal demands. This he set aside, nailing it to the cross.15 He disarmed the rulers and authorities and put them to open shame, by triumphing over them in him.”
Jesus died, rose again to life forever and now has the keys to Death and Hades.
Revelation 1:17-18 “When I saw him, I fell at his feet as though dead. But he laid his right hand on me, saying, “Fear not, I am the first and the last,18 and the living one. I died, and behold I am alive forevermore, and I have the keys of Death and Hades.”
Matthew 28:18 “And Jesus came and said to them, “All authority in heaven and on earth has been given to me.”
