While Jeffro is correct, neither Daniel nor the Babylonians used a solar calendar.
The Babylonian calendar used in Nebuchadnezzar's time (and throughout the Babylonian period) was a lunisolar calendar, meaning it was primarily based on the lunar phases, with occasional adjustments to align with the solar year, rather than a strictly solar calendar. In fact, the names of the months in the Jewish calendar are derived from the Babylonian calendar, adopted during the Babylonian exile in the 6th century BCE.
While critical scholars acknowledge connections and shared themes between the Book of Daniel and the Book of Revelation, they generally do not believe the authors of Daniel were writing about Revelation, but rather that Revelation draws upon and develops themes and imagery found in Daniel. The Book of Revelation does not directly comment on or interpret the Book of Daniel, nor does it claim to be a continuation of Daniel's prophecies. That is merely speculation/imagination on part of the Watchtower religion.
The first biblical scholar to suggest the idea of a prophetic year of 360 days was Isaac Newton. In his work, "Observations upon the Prophecies of Daniel and the Apocalypse of St. John" (1733), Newton proposed that a prophetic year, as mentioned in the Bible (particularly in the Book of Daniel and Revelation), was not the same as a solar year of 365.25 days, but rather a year consisting of 360 days.
Newton believed that this 360-day year was a symbolic or prophetic measure used in biblical prophecy. He was influenced by ancient cultures, such as the Babylonians and Egyptians, who also used a 360-day year in their calendars, which likely shaped his interpretation of the biblical text.
Isaac Newton was a devout Christian, but his religious beliefs were quite unconventional for his time. He held Arian beliefs, a view that denied the divinity of Jesus Christ as being fully God, a belief that was considered heretical by mainstream Christian denominations.
Newton based his theory on the concept that the Babylonians used a 360-day year as a symbolic or practical unit of time in certain contexts, even though their luni-solar calendar did not literally consist of 360 days in a year.
The Babylonian calendar was based on the moon's phases, meaning it was primarily lunar, with each month being roughly 29.5 days long (the average length of a lunar cycle). This resulted in a year of about 354 days (12 lunar months). To align this with the solar year (approximately 365.25 days), they would add an extra month every few years, similar to the concept of leap years, though it was not as systematically regulated as in the modern Gregorian calendar.
Some have suggested Jews had a Biblical year from various Scriptures, but their arguments do not work. Ideas that texts like Ge 7:11 imply a 360-day Jewish year are not explicit* enough to prove that Jews ever employed such a calendar themselves. Theirs was mostly lunar, as their holy days landing on the 15th (the Full Moon) of most lunar months tend to suggest (and some historians even point out that for a short time the Hebrews may have dabbled with a solar calendar).
In the end, there is no 360-day "Biblical year," like the Jehovah's Witnesses like to posit for their Gentile Times prophecy. The word "year" in Daniel chapter 4 is not the same as "period of time" in the book of Revelation written by Christians, and neither are talking about the Jehovah's Witnesses ridiculous prediction of 1914 anyway even if the two were speaking about the same thing.
Newton's idea was based on Babylon's concept, not a Jewish one--and in the end, even if all this lined up in favor of it being "Biblical," it still does not amount to Watchtower's 1914 concept.
Look at everything, look at all the different things that have to line up to make the Watchtower's Gentile Times 1914 prophecy work--no matter what you have to do, no matter what allowances you have to make, you are more likely to get a monkey to discover how to make an atomic weapon than to get all this to line up.
The Watchtower's Gentile Times prediction is manure.
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*--The 150-day period in question can also be interpreted as a period of 150 days in our modern calendar system (e.g., February 17th to July 17th) and that this doesn't necessarily prove a 360-day year.
