Answer: There is no "prophetic year" of 360 days alluded to anywhere in the Bible. It is a nineteenth century Christian invention developed through imaginative use of the Genesis flood narrative.

Some post-biblical sectarian literature and the apocryphal books of Jubilees and Enoch advocate a calendar consisting of 364 days, divided into twelve months of thirty days each. At the end of each three-month cycle a thirty-first day was added to the month. But, this is still not a 360-day "prophetic year."

Obviously, the calendar used in the Daniel 9 countdown has nothing to do with the nineteenth century development of a spurious 360-day "prophetic year."