If you read the Lord of the Rings appendices, you will find that Shirefolk do something similar: they divide the year into 12 months of 30 days each, with a four-day midsummer holiday called Lithe.
https://en.wikipedia.org/wiki/Middle-earth_calendar#Hobbit_C...
If we were to adopt a similar scheme outside of Middle Earth, I'd be in favor of borrowing the name.