[4] Divide 1,260 days by 42 months and you will get a 30-day month, as 12 months of 30 days equals 360-days in a year These time periods occur ten times in scripture: The origin appears to be in connection mainly with the following Bible verses referring to the period translated, "time".
Daniel 7:25 And I heard the man clothed in linen, which was upon the waters of the river, when he held up his right hand and his left hand unto heaven, and sware by him that liveth for ever that it shall be for a time, times, and a half; and when he shall have accomplished to scatter the power of the holy people, all these things shall be finished.
Revelation 12:14 In ancient times, twelve thirty-day months were used making a total of 360 days for the year.
[5] The Genesis account of the flood in the days of Noah illustrated this 360-day year by recording the 150-day interval till the waters abated from the earth.
We see it here in the account of the Flood: In the six hundredth year of Noah's life, in the second month, the seventeenth day of the month, the same day were all the fountains of the great deep broken up, and the windows of heaven were opened.
Genesis 7:11 And the waters prevailed upon the earth an hundred and fifty days.
§ It is noteworthy that the prophecy was given at Babylon, and the Babylonian year consisted of twelve months of thirty days.
One 365 + One 365 = Two 730 Three 1095 + Half 183 = Three Years and a half - 1278 Now if, according to this computation, we subtract twelve hundred and sixty Apocalyptical years from twelve hundred and seventy-eight Julian or Gregorian ones ( I call them so ore rotundo, overlooking the smaller measures of time), there remain eighteen years to be cut off.