There is no literal physical third temple that will be built.
The third temple doctrine comes from 2 Thessalonians 2:4.
"Who opposes and exalts himself above all that is called God, or that is worshipped; so
that he as God sits in the temple of God, showing himself that he is God."
It indeed is speaking of the man of sin, the false messiah, the Antichrist.
But it is not speaking of a literal temple.
Here is commentary from Ellicott on 2 Thessalonians 2:4.
"Though the image is drawn from the Jewish temple, we may say with some confidence that
St. Paul did not expect the Antichrist as a prose fact to take his seat in that edifice.
Neither is the metaphor to be pressed into a mere synonym of "the Church" (1Corinthians 3:17).
The words, so far need not necessarily mean that the Man of Sin will make special
claims upon the Christian community as such. Rather, the whole phrase, "taking his seat in the
temple of God," is a poetical or prophetical description of usurping divine prerogatives
generally: not the prerogatives of the true God alone, but whatever prerogatives have been offered
to anything "called God." Though the prophecy might be fulfilled without any symbolical
act (e.g., of assuming any material throne), yet the spontaneousness ("himself") and the openness
("showing himself") seem so essentially parts of the prophecy as of necessity to imply that the
Man of Sin will make formal claim to occupy that central seat in men's minds and aspirations
which is acknowledged to be due to God alone. The formal making of this claim seems to be identical
with the apocalypse of the Man of Sin, the act by which he is manifested or revealed."
So what does this mean in layman's terms? It means that Antichrist is going to be revealed in
a very grandiose way, as the Lord Jesus Christ will when He comes in the clouds and every eye will see Him.
So shall the Antichrist come, everyone will see him and know of him. All those that are not the true elect
of God will be deceived by the false messiah, the Antichrist into believing that he really is the messiah, that
he really is God. In their minds, which is what the temple of God in this scripture is referring to,
the minds of men and women, in their minds the Antichrist will actually be God to them.
So there is no end time 7 year tribulation period, and there is no literal physical third temple.
What are we looking for? Were looking for the revealing of the false messiah, the Antichrist.
He will deceive many into believing that he is the messiah, that he is God.
God's true elect, those that strictly obey His word, His commandments, His will in this life, that
have made a sacrifice of their lives to devote it to God, to live for God and not themselves, these Christians
will be martyred for their faith. Very few will survive to the end of the world when the Lord returns to
be caught up in the rapture.