What about the Stygians? In real life the ancient Egyptians built a calendar that revolved around the River Nile and the seasons of flooding, planting crops, harvesting crops. Given their knowledge of astronomy as well, do you think they might have some system in place as well? What about Khitai or Vendhya or Zamora?
I"m not saying they did or didn't but you would think that extensive arcane/astronomical/cosmological knowledge with extensive histories would result in some sort of classification for time.
I understand and accept that peasants and farmers and those not concerned with academics would stick to the traditional "seasonal" cycles of time (Winter-Spring-Summer-Fall, Solstice, Equinox, etc.) but what about those who are concerned with "higher" topics.
My 2 cents.