I will say this, 2nd Ed WFRP has a lot of neat little thing like this that do make the world more vibrant. Stuff like specific sayings and superstitions and concepts that differ from one province to another and from one faithful to another and a lot of different things that flesh out the world and make you feel that you're in a setting that is distinctly not the same as real life.
The only issue is that keeping that stuff in mind and trying to convey it to an audience that doesn't know these things can make stuff deeply confusing, which is why I think Boney hasn't talked much about it. For example, the Empire has 8 day weeks. There are 12 months in a year but the total number of days in a year is actually 400, and every month is 32-33 days. There are 6 days each year that don't belong on any particular month, defining particular days of the year (each of the equinoxes/solstices as well as Mystery and New Years, the two days a year that both Mannisleb and Morrisleb are full). Even the lunar cycle is different, with Mannisleb having 25 day cycles.
A neat fact is that the Jade Order often use a Lunar Calendar instead of the standard Imperial one. That means they count the days by Mannisleb's orbit (Morrisleb has an unpredictable and constantly shifting orbit). A year is composed of 16 months of 25 days each as a result. Tilea and Estalia also use a Lunar calendar but theirs is much more embellished with Myrmidian cultural stuff and differences from one Principality to another Kingdom to another Republic.
My point is, while it might be neat to see Panoramia use a Lunar calendar instead of the standard imperial one and getting Mathilde confused, it would equally confuse the readers who don't know about the WHF calendars. I'm not even getting into star signs, which are apparently very commonly used by superstitious peasants, so even Mathilde should know some of them.
To expand on this, I'll go through a few different calendar systems.
First, I already talked about the 8 day weeks, 12 months and general structure of the standard imperial calendar. To expand on the Tilean/Estalian Calendar, it's actually called the Verenan Calendar, as it is believed Myrmidia learnt how to track time from her mother through tracking the movement of celestial bodies, which is why a Lunar calendar is used. This calendar uses 5 day weeks, so each month is composed of exactly 5 weeks of 5 days, forming 25 day months that form 400 days when you include all 16 months. Very neat. The start date for the calendar is a topic of argument between Estalians and Tileans.
Bretonnian calendar is basically the same as the Imperial one except it starts at 924 IC after Gilles and the Companions' 12 Great Battles. Kislev have 3 calendars, the Gospodarin, Imperial and Ungol calendars. Imperial is the Empire's calendar, it's quite popular there. The Gospodarin starts the year on the Summer Solstice which they call "Shoika Day" to refer to the Khan Queen that made Kislev City. The weeks are 8 days and there are 12 months like the Empire, except the calendar starts halfway through 1524 IC on the Imperial Calendar to represent the founding of Kislev. The Ungol calendar is more inconsistent and greatly varies from place to place, but it's used by the Ungols. The calendar starts around 500 IC where the Ungol believe Ursun first awoke from hibernation. The calendar uses a four year cycle called an Urtza which has a 24 (or 26/36) month cycle.
For the other races, here's a fun fact. The human imperial calendar was cribbed from the Dwarven calendar, but the difference is that Dwarves don't separate the year into weeks and months. They count the years separately but they use "the 276th day" and stuff like that, they don't care about separation that much. They start their calendar somewhere around -5500 IC, the formation of the Karaz Ankor/creation of Karaz-A-Karak.
The Elves separate their years into 4 "Seasons". Their seasons are kind of like months, they don't have a smaller unit of measurement. The High Elves separate their seasons by Frost, Rain, Sun and Storm in that order. The Dark Elves use Blood, Despair, Decadence and Savagery. The Asrai use Ice, Rebirth, The Hunt and The Fade. The High Elves separate their calendar by the reigns of each Phoenix King, then the year of that Phoenix King's reign, then the season (represented in number), then the day. So V, 140, 3, 90 means the one hundred and fortieth year of Caradryel the Peacemaker's reign, the ninetieth day of the Season of the Sun. Dark Elves use different periods of time based on whatever Malekith feels like. Asrai separate their "calendar" into different "seasons" based on what major event they want to base the time around.
The start date for Ulthuan/Asur is the crowning of the first Phoenix King Aenarion around -4498 IC or something like that. Druchii is around -2750 IC, the start date for Malekith's betrayal. I don't want to track down the start date for Athel Loren, but their calendar starts during Caradryel's reign when they reject the call to return to Ulthuan, so after the War of Vengeance around -1600 IC.
There you go, calendars.
