Earlier quoted context omitted.
Ethiopian time keeping is peculiar all over. https://en.wikipedia.org/wiki/Ethiopian_calendar The Ethiopian calendar has twelve months, all thirty days long, and five or six epagomenal days, which form a thirteenth month.
That's similar to the Shire calendar system[1]. It has twelve months of 30 days, but the missing days are not in any month. 1: https://tolkiengateway.net/wiki/Shire_Calendar
I like that Tolkien’s legendarium got the first mention here though.