Days were understood to start at sundown instead of midnight.
Months began when the moon was “new” or “renewed” (chodesh). This required a physical sighting of the moon and would guarantee that all months were either 29 or 30 days in length.
Years were agriculture based. While they had a 12 month calendar, the length of their months required a time “reset” occasionally. As Unleavened Bread required barely, barely was the crop used to measure the years. Once it was in a state of “aviv” (nearly ready for harvest), the new year was proclaimed. If it was non “aviv,” a thirteenth month was added to the calendar so that the feat of Unleavened Bread could be properly observed. As such, their first month of the year was titled “aviv” and was the only month of the year to have been given a name prior to the Babylonian Captivity.
Links:
202408040914