The division occurs immediately,
Ar his return, he tells the goats to depart from him into the fire reserved for satan and his angels (vs 41).
Then explain this,
And to you who are troubled rest with us, when the Lord Jesus shall be revealed from heaven with his mighty angels, In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ: Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power; When he shall come to be glorified in his saints, and to be admired in all them that believe (because our testimony among you was believed in that day. 2Thes.1:7-10
And to you who are troubled rest with us, when the Lord Jesus shall be revealed from heaven with his mighty angels, In flaming fire taking vengeance on them that know not God, and that obey not the gospel of our Lord Jesus Christ: Who shall be punished with everlasting destruction from the presence of the Lord, and from the glory of his power; When he shall come to be glorified in his saints, and to be admired in all them that believe (because our testimony among you was believed in that day. 2Thes.1:7-10
A massive amount of people die from fire because, "the Lord Jesus shall be revealed fromheaven with his mighty angels, In flaming fire".
the day of the Lord will come as a thief in the night; in the which the heavenss hall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up. 2Pet.3:10
That happens after the Great White Throne Judgement (GWTJ) and LOF second death, seen in Revelation 21. There are no mortals on the planet when the NHNE happens and the old are gone.