Revelation 11:1 And there was given me a reed like unto a rod: and the angel stood, saying, Rise, and measure the temple of God, and the altar, and them that worship therein.
2 But the court which is without the temple leave out, and measure it not; for it is given unto the Gentiles: and the holy city shall they tread under foot forty and two months.
3 And I will give power unto my two witnesses, and they shall prophesy a thousand two hundred and threescore days, clothed in sackcloth.
As chapter 11 begins John is ask to measure the temple and them that worship there in but measure not the outer court for this is given to the gentiles that will have control for 42 months or 3 and 1/2 years, the second half of the tribulation.These first two verses set the stage for the second half the tribulation but as we go to verse 3 the two witnesses are introduced to prophesy for 3 and 1/2 years, which is in the first part of the tribulation.