The Antichrist being given authority to do signs & wonders along with beheading those who won't worship his image is 42 months or 1,260 days.  The Two Witnesses also have 1,260 days to prophesy and are given powers before they are killed by the Antichrist or the Beast.  

If the Antichrist's 1,260 days on Earth were exactly the same 1,260 days that the Two Witnesses prophesy, the Two Witnesses would be killed by the Antichrist after their 1,260th day which is the same day that Jesus would return with all the saints from heaven at which time the Antichrist and the False Prophet are thrown into the lake of fire and the remnant were slain with the sword that proceedeth out of Jesus' mouth which is the word of God. (Rev. 19:19-21).

However, according to Rev. 11:7-12, after the Two Witnesses are killed by the Antichrist, their bodies lie in the streets unburied for 3 1/2 days while the people of all the nations see them and are rejoicing and sending each other gifts because the Two Witnesses who tormented them that dwell on Earth are dead.  So do you really think that the enemies of the Two Witnesses are going to be rejoicing over their deaths for 3 1/2 days if at the same time the Antichrist and the False Prophet are thrown into the lake of fire and the remnant slain by the sword that comes out of Jesus' mouth?  If anything they should be in fear of their lives because of taking the mark of the beast in the forehead or the right hand and worshipping the Beast and his image.

However, if the Two Witnesses started prophesying at least 3 1/2 to 4 days before the Antichrist was given authority to do signs & wonders and authority to behead those who don't worship his image, then the Two Witnesses would be killed by the Antichrist 3 1/2 to 4 days before Antichrist was thrown into the lake of fire at the Lord Jesus' return to the Earth with all the saints.  That would give the Two Witnesses enemies the 3 1/2 days needed to rejoice and send gifts to one another while the Two Witnesses unburied bodies lie out in the open.  After which time, the Two Witnesses would be resurrected.  Therefore, I don't think that the Antichrist & the Two Witnesses 1,260 days are exactly the same 1,260 days on the calendar.