Serpent Isle Calendar

The Serpent Isle calendar is only hinted at within the Ultima VII Part Two Clue Book by the dating system used by the Xenkan Monk Thoxa. It is unknown if this data is complete, but it does give a good introduction to the calendar used on the Serpent Isle.

Overview
All weeks are divided into 5 days, with a total of 20 days per month, meaning that each month has four weeks. The days of the week are as follows:
 * Aonsday
 * Dasday
 * Triday
 * Ceithirday
 * Cuigday

The months in which Thoxa writes her diary are presented here in chronological order:
 * Montoriad, after the Sosarian twin cities of Montor.
 * Fawnehdra, after the Sosarian city of Fawn.
 * Moonehdra, after the Sosarian city of Moon.
 * Ospria, after the ship that carried the first settlers to Serpent Isle, the Osprey.
 * Sosariad, after Sosaria itself.
 * Serpentia, after the ancient, distinctly serpentine Ophidian culture.
 * Xenkaria, after the prophet and founding monk, Xenka.

The date of Thoxa's writing is 452 New Freedom, or 452 years from when the settlers left Britannia.

Observations of time-flow
The following assumes that the data is complete, meaning that all months are accounted for.

Since the days on Serpent Isle have the same length, but the year would only have 140 days compared to the 336 of Britannia, one would have to divide the years by a factor of 2.4 to find out how many Britannian years have passed (differentials in the flow of time ignored). The number would then be 188 years.

Considering that by that point it's the Britannian year 363 and the settlers have left before Ultima IV, this would indicate that there is a considerable difference in the flow of time between the two worlds. Namely, time would flow slower on the Serpent Isle than on Britannia.

This assumption does create several problems when people state their age. This is especially noticeable with Cantra, who states that she's 14, and apart from her height also looks like it, but using the before mentioned assumption about the Serpent Isle calendar, she would be at the biological age of almost 6 at 14 SI-years.