Unfortunately, common sense is what this universe is lacking, and as such in Portal High School right now I've experienced periods of time when there were seven Fridays in a row, and invitations to parties would read "12:330". And how exactly I am supposed to go to a party in a nonexistent time? And also: do I have to try to come every Friday, i.e. every day?
Seven Fridays in a row were caused by a calendar anomaly that happened in March of AG 1980. Cecil from Welcome to Night Vale speaks very negatively of the anomaly, as he assumes that it could cause a disaster that might make people forget anything before the event. Similarly, Skepness Man Beauregarde expresses dismay over this and similar anomalies, as pictured in the above quote.
The anomaly is not part of the Anno Glorii system, as Skepness Man does not mention days of the week being anywhere in it. However, details of the calendar that the Marrissaverse's general populace agrees on are largely unknown.
Welcome to Night Vale had a cultural event scheduled for each Friday, conveyed by Cecil in the community calendar. As well as that, the wedding of Lately Pirate and Ben Stiller was scheduled to occur on the third of the seven Fridays, and the seventh Friday marked the day when the debt limit had to be raised, yet again.