While an impious adventurer might get away with ignoring the events of the week of the God of a particular House, the major holidays: Carnalia, Sanguinia, Fungalia, and Magmalia are utterly unavoidable while within the city. They are a BIG DEAL, bringing in pilgrims from across the drow diaspora.
Every year the city's clergy gather at the Temple of the Dark Sea Monks to discuss the sacred progression of devotions to the city's gods. The calendar itself is not infrequently in flux as potent gods are lost or gained. There is a great deal of rivalry among priestesses for securing auspicious weeks for their temples.
The minutia of the calendar can sometimes be quite literally come down to the hour, minute, and second. Minor gods (who might have a single day of devotion) are not included in this Calendar. Some even more minor might even have particular hours devoted to their worship.
Twilight City Calendar
Every "Week" represents a Campaign Turn.
"The Blessed", if they are blessed this week, essentially have whatever Advantage exists in the RPG that is used, if rolling is ever required.