Sounds like the HS is withdrawn slowly - one person at a time. That seems very plausible to me. But when does it reach "critical mass" - "cup is full"? What decides this point? There were babies and young children in the cities that Joshua destroyed.
My own belief is that Satan would have claimed some right of control, over these children. Bringing such children into the camp of Israel would have brought the Curse with them. Doesn't mean these children will remain forever un-save-able. They can be resurrected at the 8th millennium with "the rest of the dead" (all who lived and died in ignorance of the true God and Christ). At that time, Christ will have dominion over all the earth, (and everything/every one on the earth). Curses carried from generation to generation - a sort of ownership claimed by Satan - will no longer apply. At that time each resurrected individual will have the opportunity to choose whom he will serve.
Those resurrected to judgment and execution at the Second Coming - already chose to serve The Evil One.
I think Daniel 12:7 gives the answer.
Daniel 12:7 "Then I heard the man clothed in linen, who was above the waters of the river, when he held up his right hand and his left hand to heaven, and swore by Him who lives forever, that it shall be for a time, times, and half a time; and when the power of the holy people has been completely shattered, all these things shall be finished." (NKJ)
What would it mean to "shatter" "the power of the holy people" ?? How do they stop someone who is filled with the Holy Spirit? The only ways I can think of, are imprisonment and/or death. All the disciples except John, were martyred. Some were imprisoned - all in an effort to silence them.
It seems to me, that the moment when the LAST WITNESS is killed or is in solitary confinement - THAT is when it's over (for this age).
Jeremiah - the only/last "witness" for the LORD, was thrown into a pit to die. He was finally pulled out, just as Jerusalem fell to the Babylonians.
Revelation describes the last "two witnesses". They are martyred, then resurrected by a "voice" from Heaven, and "they ascended to heaven in a cloud". I believe this is the Second Coming, because "in the same hour there was a great earthquake" (the one that splits the Mount of Olives) and the 7th trumpet sounds. (Read Rev 11:11-15 without a chapter break.)
The "two witnesses" are not just two men. I believe they will be/are Smyrna and Philadelphia (the church of the martyrs and the church of brotherly love), the last two lamps on the Lamp Stand of the heavenly Tabernacle, depicted in the vision of John.