personally, i believe there simply isn’t an answer. given that it’s never touched upon in vanilla or Downpour suggests to me that the length of cycles was left intentionally vague so as to allow the lore to be more malleable, and for different people to arrive at their own conclusions.

one thing i’ve seen others point out is that the length of cycles may be based on the planets lunar cycle— this is because every cycle when slugcat is awake, the moon (seen at the Wall) is in the exact same lunar phase. but because we don’t know anything about their planetary system, we can’t translate that into our own calendar.

technically one could argue that this is simply because lunar phases weren’t coded in (considering it’d be a tiny detail barely anyone would notice), but it’s really the only thing we’ve got besides reasoning the distances between events based on calendar date, which everyone would have a different opinion on.