Revelation 12:9 speaks of Satan being cast out of heaven to the earth. The book of Job indicates that Satan was able to enter in among the other angels at that time. Some traditions say Satan was cast out at the time of the fall in Eden. When according to Catholic teaching was Satan kicked out of heaven permanently?
At the moment of Creation, evil was separated from Righteousness.
In Ephesians chapter 3, Paul writes about the eternal plan of God: "v10 (God's) intent was that now, through the church, the manifold wisdom of God should be made known to the rulers and authorities in the heavenly realms (Satan and other angels in Job ch 1&2 etc.), v11 according to his eternal purpose that he accomplished in Christ Jesus our Lord. v12 In him and through faith in him we may approach God with freedom and confidence." (NIV; parenthetical notes are mine)
The 'when' of Satan's fall must be viewed in the context of God's eternal plan. Timing is a tricky thing. If you are viewing Satan's fall from a heavenly perspective, outside of time, it is like a lightening flash (Luke 10:18). If you are viewing it from a 'Creation' perspective, it's like a sequential argument (Job 1 and 2...) or a series of timely events (Revelation 12). Notice that Satan was created as Lucifer (Isaiah 14:12 KJV), the greatest created moral being. He became Satan when he rebelled against God. Before Creation, the only thing that existed was God... Perfection...! In Creation God made 'space' for something 'not God' to exist. Creation is not Heaven, and moral beings are not God; but we (and angels) have the ability to 'know God'; and involve ourselves with God... So in Creation we are suspended between Perfection... on the one hand, and abysmal imperfection, evil... on the other hand. This conflict between good and evil works itself out, in time, in the perfecting of our faithfulness. So in Job, God has provided the means for Job to 'maintain his integrity'; in the sin offering. In Job there is a poetic conflict between integrity and iniquity; blessings and cursing; self righteousness and the Righteousness of God, good and evil...(etc.)
Before Creation, according to His eternal plan, God knew the implications of Creating moral beings with the capacity to choose or refuse Him. And in the Atonement, the Sin Offering, the Messiah... the Creator provided the means by which moral beings can be 'right' before Him. There was no 'plan B'. So, from a heavenly perspective, at the moment of Creation, there is a separation of good and evil, like a flash... and God himself is there to provide for man and angels... From a Creation perspective, evil is at work, in Satan, persuading Adam and Eve, and Judas and Peter... And Jesus instructs us to pray: "...deliver us from the evil one..."
Well, since nothing unholy can be in the presence of God, and Heaven is in a sense being in communion with God... then a Satan who is tempting Adam and Eve to disobey in the Garden must be a Satan who is already evil himself. So at the very least, it must be prior to the temptation in the Garden.
I am on less firm ground stating that it is before the creation of the material universe, but I believe I've heard at least two people who have spiritual authority (priest and a theologian) state that. I don't have any quotations or links for you, but I can say that Angels, of which Satan/Lucifer is one, do not exist within the physical universe composed of matter and were made before our universe.
There is a Tradition that Satan's rebellion was over God's vision of creating humans, so Satan likely rebelled either just before Creation or after the universe began but before humans arose.
Also, the first expulsion from Heaven was the last. When an Angel sins its not like when we sin: Angels know the entirety of the consequences to their actions and sin with their entire will. They are so firm in their decisions that there is no repentance; so when Satan turned to Evil then that was it for him.