It’s worth noting that while the average length of the year has been quite constant over most of Earth’s history, the length of days has changed significantly.
Roughly 250 million years (1 eon) ago, the length of the day was about 23 hours and 500 million years ago (2 eons), the length of the day was about 22 hours. With the orbit of the earth around the sun being about the same length of time, that means that a year consisted of about 380 days one eon ago and nearly 400 days two eons ago. Accordingly, the length of the year will be about 350 days one eon from now. A change of just one day per year changes our calendar, so truthfully, actual calendar dates more than a million years before or after the present time would not be accurate with today’s calendar. As such, there is no point in using the quarters, days or smaller units in this calendar for any date over a million years in the future or past. The date in such cases would be most accurately represented by decimal portions of the year (i.e. Eon 19, Genesis 57, Age 4, Century 10, Year 64.525).