I am answering to present an alternate view to that presented.
The Amillenial view of end times regards the millennium as being a symbolic long period of time in the church age that the devil is locked up. The devil is released from prison at the end of the millennium and I think probably close to the end of the tribulation since it fits with the pattern of increasing evil in the tribulation and is just before the End ushered in by Christ’s return. The millennium is also a period of time where the saints rule and reign with Christ, healing the sick, winning the lost, making disciples and establishing the kingdom of God upon this world by being good ambassadors of Christ. It is important to establish how the devil being cast out of heaven fits into the sequence of bible events. When was Satan cast out of heaven?
Ezekiel 28:11
The word of the Lord came to me: 12 “Son of man, take up a lament concerning the king of Tyre and say
to him: ‘This is what the Sovereign Lord says:
“ ‘You were the seal of perfection, full of wisdom and perfect in beauty. 13 You were in Eden, the garden of God; ....
14 You were anointed as a guardian cherub, for so I ordained you.You were on the holy mount of God; you walked among the fiery stones. 15 You were blameless in your ways from the day you were created
till wickedness was found in you... and you sinned.
So I drove you in disgrace from the mount of God,
and I expelled you, guardian cherub, from among the fiery stones. 17 Your heart became proud on account of your beauty,
and you corrupted your wisdom because of your splendor.
So I threw you to the earth; I made a spectacle of you before kings.
Isaiah 14:12
How you have fallen from heaven, morning star, son of the dawn!
You have been cast down to the earth, you who once laid low the nations! 13 You said in your heart, “I will ascend to the heavens;
I will raise my throne above the stars of God;
I will sit enthroned on the mount of assembly, on the utmost heights of Mount Zaphon. 14 I will ascend above the tops of the clouds; I will make myself like the Most High.”
15 But you are brought down to the realm of the dead, to the depths of the pit.
This casting out of Satan did not occur in ages past. Jesus’s statement in John 12 fixes the time at which this happened was at Calvary. The legal basis for the devil being cast out was the finished work of Christ at Calvary.
John 12:31
Now is the time for judgment on this world; now the prince of this world will be driven out. 32 And I, when I am lifted up from the earth, will draw all people to myself.” 33 He said this to show the kind of death he was going to die.
This is further affirmed by Jesus’s prophetic words in Luke 10:18 where Jesus said he saw Satan fall like lightning from heaven.
Following Jesus’s death at Calvary he entered the strongman’s house and, He bound Satan, released his captives and took the keys of hell and the grave away from him.
Matthew 12:29
Or again, how can anyone enter a strong man’s house and carry off his possessions unless he first ties up the strong man? Then he can plunder his house.
Luke 11:21
When a strong man, fully armed, guards his own house, his possessions are safe. 22 But when someone stronger attacks and overpowers him, he takes away the armor in which the man trusted and divides up his plunder.
Revelation 1:18
I am He who lives, and was dead, and behold, I am alive forevermore. Amen. And I have the keys of Hades and of Death
Ephesians 4:11
When he ascended on high, he led captivity captive and gave gifts to his people.” 9 (What does “he ascended” mean except that he also descended to the lower, earthly regions? 10 He who descended is the very one who ascended higher than all the heavens, in order to fill the whole universe.)
Colossians 2:15
He disarmed the rulers and authorities and put them to open shame, by triumphing over them in him
Hebrews 2:14
Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil,15 and release those who through fear of death were all their lifetime subject to bondage.
Destroy in Hebrews 2:14 is the Greek word ‘καταργέω’ which can be translated “to render inactive,”“to condemn to inactivity”, “to put out of use” ,“to destroy” or “to remove from the sphere of activity” [Kittel]. This scripture together with Matthew 12:29 indicates that it is likely that Jesus entered the devils house and bound the strongman (devil) following his death and resurrection.
This is linked to Ephesians 4:11 when he led captivity captive and released hostages. We know Jesus took the keys of hell and the grave from the devil [Revelation 1:18]
The King of the bottomless pit ‘Apollyon’ could be another name for the devil. [Revelation 9:11]
Since Christ entered the devils house and bound him to release his captives. The captives are likely to be ‘the righteous dead Jews from paradise, ‘Abrahams bosom’ who like Abraham were made righteous through faith on a system of credit (Romans 4:3 accredited with righteousness through faith), but since the blood of Christ was not shed could not go to heaven, but had to stay in paradise a place of waiting for the righteous dead Jews, and thereafter were taken with Christ to heaven once his blood was shed at Calvary. Hebrews 9:26 says Jesus entered the Holy of Holy’s with his blood once for all time in the fullness of time. So this blood he shed paid for the forgiveness and sin of the Jew in OT period as well as any person saved in NT period i.e. salvation of all people for all time.
Revelation 20:1
Then I saw an angel coming down from heaven, having the key to the bottomless pit and a great chain in his hand.2 He laid hold of the dragon, that serpent of old, who is the Devil and Satan, and bound him for a thousand years; 3 and he cast him into the bottomless pit, and shut him up, and set a seal on him, so that he should deceive the nations no more till the thousand years were finished. But after these things he must be released for a little while.
At Calvary Jesus bound Satan and he was cast into the pit. During the church age Satan has ruled the hosts of darkness from the pit.
Revelation 9:11
And they had as king over them the angel of the bottomless pit, whose name in Hebrew is Abaddon, but in Greek he has the name Apollyon.
The devil therefore rules the hosts of hell from the pit. The devil is not omni-present and it is not rational to use the scripture that Satan is like a roaring lion seeking whom he may devour as proof that he is not in prison, since with billions of people on the earth he does not personally attack every Christian. I believe he has an upside down pyramid structure and his minions, principalities, powers, wicked spirits in high places, demon spirits carry out his will from the pit.
The millenium period is therefore just a symbolic long period of time in the church age between the first and second coming of Christ when the devil is bound.
If this sequence is accepted then the next event in this time period we live in is the 7 trumpets sounding, 7 bowels of wrath being poured out and 7 seals being opened. We see in Revelation a marking of the righteous and the wicked and we see 7 stages of increased demonic activity which will culminate in the devil himself being released from prison a short period before the second coming of Christ. This is what will accelerate the time of tribulation on the earth. As the sinfulness and rebellion of the wicked increases on the earth, increasing numbers of demons are released from hell upon the earth (e.g. Rev.9:3), and the point is reached where the devil is released from prison.
It is important to understand that for every bowel of wrath, there is a seal and a trumpet, so the glory upon the church increases to match the increasing darkness. The period of tribulation begins and the devil gathers to himself an army at Jerusalem (Armageddon), and at some point the Father calls time, Christ returns and the End takes place. I believe the trumpets are to call God’s people to attention to receive by faith the ministries, mantles and annointings that He is making available to His people at this time.
It is really important to prepare the Church for the next event it will need to face i.e. not rapture to heaven but the release of Satan from the pit.
Revelation 21:7
When the thousand years are over, Satan will be released from his prison 8 and will go out to deceive the nations in the four corners of the earth—Gog and Magog—and to gather them for battle.
The Church Age is brought to an "end" by the glorious return of Jesus as King of Kings and Lord of Lords (Rev 19:11-16).
At His return there is resurrection of the righteous and rapture to join Christ in his army, that immediately defeats the devil & his army. The wicked are then raised in their bodies of sin to face the White throne Judgement, and the righteous the Bhema judgement that rewards believers for fruit with motives that pass the test of fire. The wicked are cast in the Lake of fire with the devil and his angels, and the righteous are ushered into eternal life in the new heavens and new earth.