"The Anti-Christ, again mimicking Jesus sovereignty, will rule for 42 months over the earth. For three and a half years he “was given authority to continue [literally “make war”] for forty-two months” (Rev 13:5)."
https://www.whatchristianswanttoknow.com/ten-characteristics-of-the-anti-christ-according-to-the-bible/
"The 42 months refers to the reign of the Antichrist, specifically, the last half (3 1/2 years) of the seven-year tribulation. At the beginning of that time, the Antichrist will break his covenant with Israel and set up “the abomination that causes desolation” (Mark 13:14; cf. Daniel 9:27)—an act that links the Antichrist to Antiochus Epiphanes, who similarly defiled the temple. The Antichrist will then turn his attention to the genocide of the Jews. During the persecution, Israel (the woman of Revelation 12) will be protected by God in the wilderness. Also during that troubled time, God will send two witnesses to perform miracles and proclaim the truth of Christ in the face of the Antichrist’s lies (Revelation 11:5–6)."
https://www.gotquestions.org/prophecy-1260-days-Revelation.html
"Notice in verse 5 that we are told the antichrist will have total power for 42 months. That is, 3.5 years. The message is he will insist that the world worship him during the last half of the tribulation. This reveals that he wants to be like Christ. He will want total control and have everyone worship him. He will truly be anti or against Christ. For 3.5 years he will rule the world, but he will be faced with one major crisis after another."
https://www.neverthirsty.org/bible-studies/book-of-2thessalonians/what-will-the-antichrist-do/
"He apparently assumes world dominating power three and one-half years after he confirms the covenant. He then will continue his reign for 42 months-Revelation 13:5."
https://www.endtime.com/antichrist/