The Calendar appears in Suikoden Tactics. There are 360 days in a year, with 72 weeks and 12 months per year. There are 30 days and 6 weeks in a month and 5 days per week. The names of those days are Firesday, Watersday, Windsday, Earthsday and Lightningsday. On every respective day, there is a specific elemental monster appearing in the Ruins of Obel chamber. Months are usually called by simple number.
Firesday → Windsday → Earthsday → Lightningsday → Watersday
Note: The cycle repeats after Watersday.