At what point in time and creation did Satan (Lucifer the former arch angel) along with all the other angels who followed him fall from God's glory and caste out of the heavenly realm? Also which act is it that they (Lucifer and the angels who follow him) do that makes God condemn them from the glory and reign of heaven. I know in the garden of Eden he was condemned as a serpent but had he already been a fallen angel by then or was it not until later, possibly when "the sons of God" sought after the daughters of man and created the Nephilim in Gen. 6 that they were cast out?
The Bible does not give a specific account of when Satan and the fallen Angels were ejected from Heaven, but we are given some clues as to a timeframe.
All Scripture is quoted from the King James translation.
Isaiah 14:12-14 KJV
Isaiah chapter 14 tells us why , and gives us a clue as to when. Lucifer tried to usurp the position of God, and take over Heaven and that is the reason. The clue comes in the being cast down to the ground. If Satan was cast to the ground it had to be after:
Genesis 1:9 KJV
until the third day there was no dry ground.
Jesus gives us another clue in:
Luke 10:18 KJV
Jesus tells us he was present and that Lucifer and Satan are one and the same.
The rest we get in the Revelation:
Revelation 12:3-4 KJV
The red Dragon here refers to Satan and the part about his tail casting one third of the stars to the ground refers to one third of the Angels rebelling with Lucifer and being cast to the Earth with him.
Lastly as you stated in your question Satan was behind the serpent tempting Eve.
So using those clues we can only determine that they were cast out of Heaven after the second day of creation and before the fall of mankind.
The bible does not provide a specific date for creation. Ussher Chronology proposes 4004BC. Angels were created before the earth and man.
Job 38:7 KJV
Lucifer was a covering cherub.
Ezekiel 28:7 KJV
Lucifer's desire for self-exhaultation led to rebellion against God. He seduced a third of the angels to follow in his rebellion.
Isaiah 14:12-13 KJV
Ezekiel 28:15-18 KJV
Revelation 12:4 KJV
Lucifer was condemned before the fall of man. The serpent was the medium through which deceit was practiced. Sons of God and daughters of men. The phrase sons of God depict the righteous.
Hosea 1;10 KJV
John 1:12-13 KJV
Romans 8;14 KJV
Daughters of men depict the wicked.
Ecclesiaste 8:11 KJV
The premise that the sons of God are fallen angels is error. Further, angels do not procreate.
Genesis 6:2 KJV
does not mention giants. However,
Genesis 6:4 KJV
Obviously, there were giants in the earth before the sons of God.
Job mentions the place of fall.
Job 26:13 NIV
He paints on the same picture as we got in genesis 1 where the Spirit of God moves upon the waters above