If they believed in a future Sabbath day, why would they think Satan would not be bound also at that point? Are you saying they think Satan will be loosed and walking around on earth for 1,000 years?
Ancient Chiliasts had a very rigid system of eschatological belief in 7000 literal rigid years of human history. After this, they believed the redeemed were into the new heaven and new earth. That may explain why “time” comes to an end right at the very completion of their future millennium and how they make no allowance for Satan’s little season.
Another strong reason why they did not accept Satan’s little season at the end was because of their expectation of a future millennium. They saw it as a perfect pristine unspoiled arrangement that was liberated from all the bondage of corruption. That meant they saw no sin or sinners, no decay or disease, no dying or crying, no devil or his demons.
They believed that Satan and his demons were destroyed at the second coming. It is not just that the ECFs believed Satan was bound at the First Advent, not one early writer that I can find (up until AD240) taught a further binding of Satan at the second coming. You are trying to foist that upon them without the slightest evidence (or justification) to do so. What is more, they believed the devil and his angels were destroyed at the second coming. So, there was no evil one to populate the age to come and no wicked to deceive. This too is akin to modern day Amil. Think about this: for 210 years after the death of Christ all the Fathers anticipated a perfect age to come free of the bondage of corruption and free of all rebellion in the visible and invisible realm.
It is certainly significant that there was a widespread acceptance among the early Chiliast writers that Satan was bound through the earthly ministry of Christ. But what runs hand-in-hand with that is the fate of Satan when Jesus comes. The most startling thing about the beliefs of the earliest Millennialists who spoke of this is that they believed Satan, his minions and all evil would finally be eliminated at the second coming. This is extremely surprising because it runs totally contrary to what is loudly taught today by all modern Premillennials, of all sections. An obvious and vital by-product of that is that it eliminates the whole idea of Satan’s little season 1,000 years after the coming of the Lord. This is undoubtedly a curious position, allowing for the actual detail of Revelation 20. This suggests that early apostate Judaism had a greater influence on the formulation of this early Chiliasts theory than Revelation 20. In fact, early Millennialists seem to have acquired many of their core early beliefs from Christ-rejecting Judaism.
Justin Martyr
One of the leading early Chiliast proponents of this was Justin Martyr. He believed that Satan would be destroyed at our Lord’s return:
[T]he serpent that sinned from the beginning, and the angels like him, may be destroyed, and that death may be contemned, and for ever quit, at the second coming of the Christ Himself (Dialogue with Trypho, Chapter 45).
This couldn’t be clearer! This ancient writer depicts the termination of all evil at the glorious return of Christ. Justin explains how Satan, his angels and death itself are destroyed at the second coming of Christ. This allows no room for the Premillennialism scheme where Satan is bound 1,000 years after the second coming and then released to gather Gog and Magog to fight Christ and the glorified saints. Not only is Satan and his minions and death destroyed at Christ’s coming, but, all the bondage of corruption is destroyed. He teaches that there shall be “freedom from suffering, from corruption, and from grief.” This, paradoxically, is one of the main dividing points between Amillennial/Postmillennial teaching and that of Premillennialism reference the appearing of our Lord.
He further states in another work:
For the prophets have proclaimed two advents of His: the one, that which is already past, when He came as a dishonoured and suffering Man; but the second, when, according to prophecy, He shall come from heaven with glory, accompanied by His angelic host, when also He shall raise the bodies of all men who have lived, and shall clothe those of the worthy with immortality, and shall send those of the wicked, endued with eternal sensibility, into everlasting fire with the wicked devils (1st Apology, Chapter LII).
The second coming sees the elimination of every enemy of righteousness. The coming of Christ is climactic. In the eyes of most of the earliest Chiliast writers there was no allowance for sin and Satan, crying and dying, Satan and his minions on a future millennial earth. It is a new perfect porchway into the eternal realm.
For among us the prince of the wicked spirits is called the serpent, and Satan, and the devil, as you can learn by looking into our writings. And that he would be sent into the fire with his host, and the men who follow him, and would be punished for an endless duration, Christ foretold. For the reason why God has delayed to do this, is His regard for the human race. For He foreknows that some are to be saved by repentance, some even that are perhaps not yet born (1st Apology of Justin, Chapter 28).
According to Justin, the seeming delay in the return of Christ is for the special purpose of the salvation of souls. But when this occurs, he indicates the punishment of Satan, his devils, and the wicked occurs. The fate of all of these are carefully tied together. They are all punished at the same time. He states in the same book:
[Y]ou hesitate to confess that He is Christ, as the Scriptures and the events witnessed and done in His name prove, perhaps for this reason, lest you be persecuted by the rulers, who, under the influence of the wicked and deceitful spirit, the serpent, will not cease putting to death and persecuting those who confess the name of Christ until He come again, and destroy them all, and render to each his deserts (Dialogue with Trypho, Chapter 39).
Once again, the second coming is presented as the time when the devil and all evil come to an end. This is clear and repeated in the teaching of these early Chiliasts.