Implementing a non-terrestrial calendar
There are several non-Gregorian calendar classes derived from System.Globalization.Calendar within the Globalization namespace (i.e. JapaneseCalendar). You should be able to implement your own. I'd whip up a sample, but there are 16 abstract methods in the Calendar class...
You might even be able to simply derive your class from GregorianCalendar and just override the GetMilliseconds(DateTime) method, returning the base's return value multiplied by 1.027d.