The basic measure unit of dwarf calendar is twenty four hours. The length of it can differ because it generally depends on the sun. That is why the dwarf calendar day lasts from sunrise until sunset.
Moreover the dwarfs know calendar years. The dwarf calendar year starts when the days become longer that is during the winter solstice. It is either on 21 or 22 December and it depends on the particular year. Long celebration of the New Year’s Eve and giving each other presents led to the legend that dwarfs help Santa Claus (who arrives two days after the dwarf New Year’s Eve).
The dwarfs tackled the problem practically and divided years into shorter time periods. They stick to the ten days units (which seems basically logical if you use the decimal system) and seasons.
There is no denying that due to these changes their calendar is much simpler than the Gregorian one.