It is the 70th week of Daniel and is therefore of seven years duration.

DANIEL 9:27- AND HE WILL MAKE A FIRM COVENANT WITH THE MANY FOR ONE WEEK, BUT IN THE MIDDLE OF THE WEEK HE WILL PUT A STOP TO SACRIFICE AND GRAIN OFFERING; AND ON THE WING OF ABOMINATIONS WILL COME ONE WHO MAKES DESOLATE, EVEN UNTIL A COMPLETE DESTRUCTION, ONE THAT IS DECREED, IS POURED OUT ON THE ONE WHO MAKES DESOLATE. 

Half the period is said to be 42 months or 1,260 days.

REVELATIONS 11:2-3- LEAVE OUT THE COURT WHICH IS OUTSIDE THE TEMPLE AND DO NOT MEASURE IT, FOR IT HAS BEEN GIVEN TO THE NATIONS; AND THEY WILL TREAD UNDER FOOT THE HOLY FOR FORTY-TWO MOUTHS.  AND I WILL GRANT AUTHORITY TO MY TWO WITNESSES, AND THEY WILL PROPHESY FOR TWELVE HUNDRED AND SIXTY DAYS, CLOTHED IN SACKCLOTH.