pmmg
Myth Weaver
If the underground dwarf kingdom is open to trade there must be some number of dwarves who know everyday when the sun is up because they can look out the front door and see it. those dwarves might have to live by the same schedule as surface dwellers but the rest may either get their time from their relation with those our may have other systems to guide them other than sleep such as a qouta...mine so mure ore than do what you want till you get sleepy.