Age of the God Towers
The Age of God Towers uses the Greyhawk calendar:
The Greyhawk year consists of 364 days, split into twelve months of twenty-eight days each, and four seven-day festivals, each placed at three-month intervals. Different cultures in the campaign setting have their own names for the months and festivals. The months and festivals are commonly referred to as the Dozenmonth of Luna and the Four Festivals.