After the Mighty Angel had given John instructions on measuring the Temple, He said 'And will give power unto My Two Witnesses, and they shall prophecy a thousand two hundred and threescore days.'

         That is equal to 42 months of 30 days each, or 3 1/2 years, then is the time when the two witnesses are to prophesy which is the last half of the Week, or 7 years, the time of the Great Tribulation.