The third temple is spoken of in the OT book of Daniel. His vision of the end times correlates to John's vision in Revelation. Daniel says the anti-Christ will put an end to sacrifice. In order to put an end to sacrifice there must be a Temple. There is only one place on earth the Jews can sacrifice and that is the Temple. He also says the anti-Christ will set up an abomination on a wing of the Temple. It will be rebuilt.
You might study Daniel separately..
The antichrist did put an end to sacrifice and the Temple in 70 AD.
The Abomination was raised by Antiochus.
Revelation 21: 22 says there is NO Temple because Jesus is the Temple.
I beg to differ. Daniels vision and John's vision both concern the end times. As for the temple, you may want to read verse 10 which refers to the New Jerusalem coming down out of heaven from God. Of course at that time there will be no need for a temple because Jesus is the temple.
The New Jerusalem is spiritual..
Most of what John of Patmos wrote in his letter to the 7 churches happened within a generation.