In the world of Andrzej Sapkowski's Witcher books, how many days long is a year? How many days long is a synodic month (the average time between two full moons)?
I used to assume that the stories take place on an alternate Earth with the same astronomy as our Earth. That is a convenient default for fantasy stories, and is supported by the books using our month names. However, The Tower of the Swallow (Wieża Jaskółki) chapter 1 seems to contradict this, because it states that the moon is always waning on the autumn equinox. On Earth, the moon phases at the same date of the year keep changing quickly enough, even short-lived humans would notice that they differ within a decade.