All dates in the bible are expressed in terms of the Biblical Lunar Calendar, except for time periods which run entirely after 1992Elul where the New Biblical Lunar Calendar (the NBLC which starts in the Hebrew month of Elul) is used. #1 This calendar was the universal calendar of early man. It is not something dreamt up by the holy spirit for the bible. It is what all civilisations used prior to 800 BC. The BLC has 360 days in each year and has 30 days in each of its 12 months. It applies from Genesis to Revelation.
11 In the 600th year of Noah’s life, in the second month, on the 17th day of the month, on this day, all the springs of the vast watery deep were broken open and the flood gates of the heavens were opened
24 And the waters continued overwhelming the earth 150 days. (Genesis 7 NWT) (Genesis 7)
3 And the waters began receding from off the earth, going and receding, and at the end of 150 days the waters were cut short/diminished/lacking/without (sufficiency to overwhelm the earth).
4 And in the seventh month, on the 17th day of the month, the ark came to rest on the mountains of Ararat (Genesis 8)
The bible uses the expression: A month of days, 4 times...
20 but up to a month of days, until it comes out of your nostrils and it has become a loathing to you, just because you rejected Jehovah, who is in your midst, and you went weeping before him, saying: Why is
it that we have come out of Egypt?'
21 Then Moses said: The people in the midst of whom I am are 600,000 men on foot, and yet you -- you have said, 'Meat I shall give them, and they will certainly eat for a month of days'! (Numbers 11 NWT).
13 and remove the mantle of her captivity from off her and dwell in your house and weep for her father and her mother a month of days and after that you should have relations with her, and you must take possession of her as your bride, and she must become your wife. (Deuteronomy 21 NWT)
13 As for Shallum the son of Jabesh, he became king in the 39th year of Uzziah the king of Judah, and he continued to reign for a month of days in Samaria. (2 Kings 15 NWT)
So a month has a specific number of days in it. That number cannot be 31 days because then there would not be too many day in the year and non intercalary month. So it is 30 days given that we now have 365¼ days in the solar year.
The first BLC calendar used from the time of Adam onwards, started the year on Tishri1. This was because Adam was born in Tishri. The Jews still celebrate their new year, Rosh Hashana, on Tishri 1 today. The second BLC, which began to be used by God's command in 1513 for sacred matters, after the Passover in Egypt, started the year on Nisan1.
The biblical BLC starts the year by fixing the passover, which is the 14th day of Nisan. This must be in spring, i.e. after the vernal equinox. Nisan is the first lunar month to have a 14th day after the vernal equinox.
The early Hebrew, Roman, Egyptian, Mayan, Chinese and Babylonian Calendars were all likewise 360 days long with 12 months of 30 days each. This is why the circle has 360 degrees in it.
Plutarch: "During the reign of Romulus ...they only kept to the one rule that the whole course of the year contained three hundred and sixty days." Plutarch. (A.D. 75) Translated by John Dryden.
Plutarch: "Hermes playing at draughts with the moon, won from her the seventieth part of each of her periods of illumination, and from all the winnings he composed five days, and intercalated them as an addition to the 360 days." Plutarch. Isis and Osiris (c. A.D. 80) Translated by F.C. Babbit
As regards the Ancient Egyptians, they started the year when the star Sirius came over the Eastern Horizon just before Sunrise. But according to Goudsmit, Samuel A. Time. New York: Time Incorporated, 1966. p. 69.
Goudsmit: "They also kept a separate year made up of 12 fixed 30-day months...Later, to make their lunar year jibe almost precisely with Sirius' rising, they tacked five extra days onto the year."
As regards where the extra 5 days in the Solar year came from:
Goudsmit: "To account for them they created the myth of Nut, the sky goddess, who had been unfaithful to her husband, Re, the sun god. In retribution, Re decreed that she should bear a child 'in no month of no year.' But Nut's lover Thoth played dice with the moon and won five days a year. Because these days were outside the calendar, Re's decree did not apply. Nut's son was born on the first of them."
The Book of Calendars edited by Frank Parise states as regards the Egyptian Calendar:
Parise: "This 360 day calendar, like so many others, was changed during the 8th century B.C. to one of 365 days. The extra five days was simply added to the end of the year."
The Egyptian calendar was the first solar calendar and contained 365 days. These were divided into 12 30-day months and five days of festival (Neugebauer 1969).
The same book states as regards the Chinese circle:
Parise: "The number of degrees...does not add up to 360 because in the 4th century B.C. the Chinese astrologers suddenly changed the division of the circle from 360 degrees to 365 degrees 15 minutes."
Latin America (historical): The advanced cultures in Latin America used a ritual calendar with a period of 13 times 20 days in combination with a solar year that consisted of 18 months with 20 days each plus five extra days (which were considered calamitous). This resulted in a 52-year cycle. In general, there was no continuous count of the years. Only the Maja (Mayans) counted the years, starting from 3114 BC (Julian) in units of 'kin' (1 day), 'vinal' (20 days), 'tun' (360 days = 18 vinals), 'katun' (7200 days = 20 tuns) and 'baktun' (144000 days = 20 katuns). www.maa.mhn.de/Scholar/calendar.html
Sir Isaac Newton stated:
"All nations, before the just length of the solar year was known, reckoned months by the course of the moon, and years by the return of winter and summer, spring and autumn; and in making calendars for their festivals, they reckoned thirty days to a lunar month, and twelve lunar months to a year, taking the nearest round numbers, whence came the division of the ecliptic into 360 degrees." (Anderson, Robert. The Coming Prince. London: Hodder & Stroughton, 1894. )
The truth about the biblical 360 day year as mentioned by Newton was quoted by Sir Robert Anderson in his book, The Coming Prince, page 68. This was not a new discovery by Sir Isaac Newton in the late 1600s or even by Sir Robert Anderson in 1895. It was clearly discussed in detail by Christian, Julias Africanus in his Chronology in his explanation of the fulfillment of Daniel's Seventy Weeks, written about A.D. 240.
In order for the year to be 360 days long the day has to be longer than it is now in the ratio 365.2421897/360 = 1.01456164:1 = 1.456164% larger. In other words rather than being 24 hours long it would be around 24.35 hours long. How could this have been the case? Well when an ice skater spreads her arms out she rotates more slowly and when she draws them in she rotates more quickly. If the earth spread out a bit and got fatter at the equator and flatter from pole to pole (as if someone was treading on a basketball) then it would rotate more slowly and so the day would last longer. But the earth is actually fat at the equator and squashed at the pole due to centrifugal force and the liquid nature of the earth under its crust. So if the planet were hotter then it would be more liquid and so the centrifugal force arising from its rotation would cause it to expand and be fatter at the equator. Now before the flood this was the case. The flood dumped a load of water from the atmosphere onto the crust of the earth which would have cooled the earth down and therefore stiffened it up and reduced the bulging effect of centrifugal force. So we propose that prior to the flood the circumference of the earth was larger than it is today.
http://www.ancient-world-mysteries.com/360-days.html makes an overcomplicated presentation of a fascinating finding namely that a geographical mile (which is the distance on the equator traced out by one second of arc which is one 60th of a minute of arc which is one 60th of a degree of arc which is on 360th of a circle) would in fact be almost precisely 6,000 feet long rather than the present 6,087.253 feet long if the earth was indeed 1.456164% larger in circumference and therefore the day was 24.35 hours long and the year had 360 days in it. This is because 6,087.253 is 1.45421% larger that 6,000.
This all works because the circumference of the earth is linearly related to the period of its rotation around its axis for small variations from the present 24 hour day period in order that angular momentum is preserved. For if we keep the velocity of its surface the same then for small variations in day length we preserve angular momentum which is the integral of mass x velocity for each particle of the planet. So to increase the day by 1.456164% we increase the circumference of the earth by the same amount.
So we propose that the flood waters cooled the surface of the planet down by such an amount that it stiffened up to such an extent that the centrifugal force of its own rotation caused it to bulge by 1.45% less. Hence it span 1.45% faster. Hence the days became 1.45% shorter. Hence the year contained 1.45% more days. It increased from 360 days to the present 365.2421897.