42 months

three and a half years

42 months = 3.5 years

First half of tribulation

Revelation 11:3

And I will give power unto my two witnesses,

and they shall prophesy a thousand two hundred and threescore days,

clothed in sackcloth.

Second half of tribulation

Revelation 12:6

And the woman fled into the wilderness,

where she hath a place prepared of God,

that they should feed her there a thousand two hundred and threescore days.