A challenge for fantasy writers is creating a believable world. For the most part the world of which Mídhris is a part operates by the same laws of physics and geological and historical developments as the word we know, good old Terra. The planet is the same size as earth, with very similar lengths of days and years.
Because it is fantasy I can play a bit. I can also simplify. So the Mithron calendar has 365 days, with no remainder and thus no leap years. From there, of course, the rest is human convention. Twelve months of thirty days each with five intercalary days.
The intercalary days are the first day of the year -
Rushlatha, Birth Day [of the year] - which falls on the winter solstice; the vernal equinox -
Fuhllatha, Blood Day [from the memory of fertility sacrifices no longer made]; the summer solstice -
Shachlatha, Sun Day; the autumnal equinox -
Veshlatha, Harvest Day; and the last day of the year -
Baslatha, Death Day.
The months are as follows:
Odnaj - the Snow Month
Ardhaj - the Bear Month
Agraj - the Opening Month (when buds appear)
Daordhaj - the Bee Month
Kjoraj - the Cherry Month
Vechtaj - the Herb Month
Gwenthaj - the Wheat Month
Selivaj - the Plum Month
Enskaj - the Dancer's Month (when Senjir the Dancer appears in the heavens)
Veshnaj - the Harvest Month
Helaj - the Hunting Month
Dorchaj - the Dark Month
Before you panic trying to vocalize these names, remember that "J" always has the sound of "Y." The months all end with the syllable "aj" which sounds a lot like "eye" but with an extra "y'" at the end.
Another time we can consider the lunar cycles and weeks. The zodiac takes us into the star faith of Mídhris and its mythology.
Everything in the stories is plotted with the date, moon phase, constellations, and weather in mind. If I can't believe it, neither will you.
--DMG