All months have 30 days -- four weeks, each with seven days, named numerically (Firstday, Seconday, Thirday, etc). The two extra days fall between the second and third week, and the last and the first of the following month. These are called First- and Last Freeday.
There are five holydays that fall between the months.
Months and holydays: Primium
Secundum -St. Eleina's Day Tersium Quartum -St. Servin's Day Quintum Sextum
Octavum - Harbringer
Novium Decadum - St. Revan's Day Undecium Dodecium
The years are counted as Year of Enlightenment (YE), with YE 0 being the first year after the signing of the Covenant.