I just encountered a curious concept on the web. Apparently some Christian eschatologists promote the idea that in Ancient Israel, time was calculated according to a "prophetic calendar" of 360 days.
[Hebrew Zodiac mosaic excavated in a 5th Cent. synagogue]
So I researched this concept using every tool available to me. And my conclusions? Not to put too fine a point on this but - Norishkeit. Nonsense. Hogwash of the most unkosher variety. I looked in vain across a half-dozen sites devoted to this "calendar" for a single prooftext or valid Biblical citation establishing that any Israelites, let alone the prophets, ascribed to such a calendar - and, of course, I found none.
What I did find was a lot of calculating based on, and references to, Daniel, Chapter 7. Seems that what drives this bit of astronomical sleight-of-hand is neither Biblical notions of time nor ancient Hebrew calendar controversies, but an anxiety over the fact that the numbers of years that actually transpired between the destruction-restoration of the Temple and any likely birthday dates of Jesus (4 BCE and 6CE being the most viable contenders, with 1CE enjoying little confidence from moderns) does not match up with the numbers appearing in Daniel concerning a period of "seventy weeks." These "weeks" are taken to refer to years, so the timetable* for the run up to Jesus "has" to be 490 years. But that doesn't really work, whether one uses the actual solar years or the actual lunar years (365.2 or 354.4 [rounded] days) that transpired, so it became necessary to construe a "prophetic year", allowing Christian exegetes to redivide the total number days into 490 artificially constructed 360-day years, causing actual history to be forced into a Procrustean bed of Christocentric time.
To the best of our knowledge, there were three revisions of the calendar over the Biblical period. We start with a Canaanite calendar (I Kings 6:1; 8:1; 6:38), had some kind of reformation of the calendar in the 6-5th Centuries BCE (Jeremiah, II Kings, Ezekiel), but then adopted other revisions from the Babylonians post-exile (Haggai, Zechariah, Ezra) . But none of them involved a "prophetic" system as described by these sites.
Which is not to say ancient Jews did not have real sectarian disputes about the calendar. The chief of these being a competition in Greco-Roman antiquity between the Luni-Solar (12 lunar months adjusted to the solar year by the periodic addition of a leap month) vs. a Solar calendar of 364 days (4 seasons x 13 weeks of seven days) promoted by certain Priestly-centered ideologies. The Luni-Solar calendar is, of course, the calendar Jews use today. But the evidence of 1st Enoch, Jubilees, and the Dead Sea Scrolls indicates that the authors of these works believed this 364-day calendar was an angelically authorized calendar, while the calendar based on the cycles of the moon was an infernal contrivance. Thus we find in I Enoch (chapter 8) that the list of pernicious things that the fallen angels taught primordial humanity include:
....6) Akibeel taught signs; 7) Tamiel taught astronomy; 8) And Asaradel taught the motion of the moon....
The priestly writers who composed the sectarian writings among the Dead Sea scrolls also rail, far more explicitly, against the evils of the lunar-based calendar .
And it is interesting to note that how we apply the calendar still causes sectarian controversy among Jews. The traditional observance of holidays to this day include a extra day of Moed (Festival start), a residual practice of the time when the calendar was calculated by direct observation of the moon and was, therefore, subject to ambiguity.
But once a mathematical means of determining the months and holidays was developed and refined by the 5th Cent. CE, the functional "need" for second-day observances abated. Still, 1500 years after the resolution of the problem, when the 19th Century Reform movement included among its reforms the elimination of the yom sheini, (second day) of moed, Reform was declared anathema for it by many traditionalists. So the Jewish calendar still provides occasion for controversy, even to this day.
Zal g'mor - to own the Encyclopedia of Jewish Myth, Magic, and Mysticism, go to: http://www.amazon.com/Encyclopedia-Jewish-Myth-Magic-Mysticism/dp/0738709050
* This timetable does not concern modern Iraq, so I'm going to ask Senator McCain to please stop flaming me.
 Morgenstern, J., "The Three Calendars of Ancient Israel," HUCA, 1, 1924.
 Elior, R., The Three Temples, 2004