Satan’s fall from heaven is described in Isaiah 14:12-14 and Ezekiel 28:12-18. While these two passages are referring specifically to the kings of Babylon and Tyre, they also reference the spiritual power behind those kings, namely, Satan. These passages describe why Satan fell, but they do not specifically say when the fall occurred. What we do know is this: the angels were created before the earth (Job 38:4-7). Satan fell before he tempted Adam and Eve in the Garden (Genesis 3:1-14). Satan’s fall, therefore occurred somewhere after the time the angels were created and before God created the foundations of the earth, which include all the things necessary to sustain life on the planet, ie; gravity, the shape of the planet, oxygen, water, the axis, earths rotation, atmosphere, etc. These are referred to as anthropic constants which there are 122. Satan was on the planet years before he tempted Adam and Eve in the Garden, Scripture does not specifically say when.
Satan fell because of pride. He desired to be God, not to be a servant of God. “How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations! For thou hast said in thine heart, I will ascend into heaven, I will exalt my throne above the stars of God: I will sit also upon the mount of the congregation, in the sides of the north: I will ascend above the heights of the clouds; I will be like the most High. Yet thou shalt be brought down to hell, to the sides of the pit.” Isaiah 14:12–15
Ezekiel 28:12-15 describes Satan as an exceedingly beautiful angel. Satan was likely one of the highest ranking of all angels, the anointed cherub, the most beautiful of all of God's creations, but he was not content in his position. Instead, Satan desired to be God, to essentially “kick God off His throne” and take over the rule of the universe. Satan wanted to be God, and interestingly enough, that is essentially what Satan tempted Adam and Eve with in the Garden of Eden (Genesis 3:1-5). The reference to Satan’s fall is actually not an accurate description. It would be far more accurate to say God cast Satan out of heaven (Isaiah 14:15; Ezekiel 28:16-17). Satan did not fall from heaven; rather, Satan was pushed.
“And there was war in heaven: Michael and his angels fought against the dragon; and the dragon fought and his angels, And prevailed not; neither was their place found any more in heaven.” Revelation 12:7-8