Different sized hourglasses on each of the faces could delineate certain units of time. (One hour glass would be an hour, one a half hour, one 2
hours, etc.-- all clearly labeled of course).
Just set the time unit you want to measure facing up, and away you go.
Sounds like maybe a religious artifact to me. Maybe the reason for little evidence is because they are from mystery cults?
Or maybe it represents a divination system or an astrology system?