When did Satan fall?
Satan sinned when he became prideful and wanted to be like God. Read the passage about Satan.
How you have fallen from heaven, O morning star, son of the dawn! You have been cast down to the earth, you who once laid low the nations! You said in your heart, “I will ascend to heaven; I will raise my throne above the stars of God; … I will make myself like the Most High”.
When Satan sinned he was cast out of heaven. No one knows for sure the time of this event, but the common thinking is that this had to be after day 6 of creation because God created everything good, and Satan’s rebellion would not have been good. Plus, it had to be after God created earth because that is where Satan was cast to. In Genesis 1:28, God commanded Adam and Eve to be fruitful and multiply. If they waited too long they would have disobeyed God. So it could not have been very long after the creation week that Satan fell and tempted Eve.