Once we get off the surface of the earth, seconds are more useful than days. Or, more likely, Ksecs and Msecs. A kilo-second is 16.67 minutes, 100 Ksecs is 27.7 hours, an Msec is 11.57 days. 30 Msecs is 95% of an Earth year. These are all useful measures for humans to work in.
Financial and similar institutions would likely treat the festival day(s) as they do any long weekend at the moment. Pay cycles could be adjusted with end of year 'bonus' to cover out of cycle days.
I'm sure there's something but we've dealt with quirky calendars for a long time so really we're just attacking the same problem that we currently have with 30 day fixed cycles.