I have a question.
Have any Galbarian cultures done any astronomy yet? My characters probably won't introduce it IC, I'm just curious.
Gerrik did a bunch of astronomy, and still likes to star-gaze, although since Gerrik hasn't yet been introduced to mathematics it is entirely phenomenological. This information has spread, and was actually one of the reasons Fiberslayer had the Chipper-genocide way back (back at the first post which mentioned the Chippers). This probably won't have resulted in a calendar yet, but will have sparked some interest of astronomy, especially among Chippers.
But as already mentioned, the Vetruvians and urtelem both have their own calendar systems. The urtelem stone calendars will work best for making an actual calendar, because it is linked to the position of Galbar in its orbit around the sun.
Re: Time/date for posts. Let us not attempt to retrospectively date posts, because that is more effort than it is worth.
And let us also not make portions of Galbar have time flow at different rates to other portions of Galbar, because what happens if you travel from one place to another, and what of Galbar's orbit around the sun? Such an ad-hoc explanation is asking for trouble.
However, I do feel that approximate dates will be useful, especially when relative to a major event (eg. the Realta invasion). This gives a consistent passage of time and a proper indicator of age. For instance, I have no idea how old Gerrik is. My original head-canon put him as just a hundred or two years old, but he's been around long enough IC, from the invention of fire to present day, that he is probably much older. While it will be a hellish effort trying to retcon the dates of older posts, adding dates to posts here-after will be handy.
Additionally, adding dates for your own posts is not too difficult. First, find a dated event. Second, figure out how approximately long after that event your post will have taken place. For example, let the Blinding Purge be our reference event, since this was a global event of global significance that happened over an extremely brief period of time (one or two days).
Looking at Gerrik's timeline, Gerrik was in Fibeslay at the time of the Blinding Purge, and left immediately after. He traveled some distance, possibly for a year or two (I haven't figured out how quickly Gerrik typically travels), then settled down in Tallgrass, where he has been for maybe half a year.
Looking at the Xerxes battle timeline, preparations for war have been ongoing in Alefpria since the Blinding Purge. Lifprasil received Father Dominus at that time. Production of Cosmic Knights began once Alefpria received refugees of the Blinding Purge, as indicated by the Twins post (so some weeks later). Concurrently, Tauga enacted a coup of Xerxes some time after (probably soon after) the Blinding Purge. Xerxes was under her control for some time. Then Amartia returned. Xerxes fell into revelry for 30 days, then came the blood rain and Xerxes began preparations for war immediately. While the period of Tauga's dictatorship is somewhat ambiguous (Termite can clarify it if necessary), the battle will probably occur approximately one year after the Blinding Purge (at this rate).
Although this brings up a small matter of units of time. The year and day are obvious, since they tie into physical motions of Galbar. However, the 'week' and 'month' are not so relevant to Galbar. Galbar has multiple moons, each likely having different orbital periods, so using the phases of the moon to denote time would be rather ambiguous. It could be done, but would be inconsistent across cultures depending on choice of moon. Additionally, to my memory, no Galbaric religious traditions have been established regarding any periods of time shorter than a year. This leaves no established consistent unit of time between day and year for Galbar.
