The other day I stumbled upon this old thread: https://www.spellsofmagic.com/read_post.html?post=269041
One of the replies states that the Seelie Court rules from May 1st to October 31st, and that the Unseelie Court rules for the other half of the year.
i always try to crossreference information, soI looked into it, and the only source I could find was a site called fairyblossomfestival.com, which seems to be a real life fantasy game of some sort, and not much of a reliable resource as far as researching actual folklore goes.
I thought it might be a reference to the Spring and Summer Courts for the Seelie and Autumn and Winter Courts for the Unseelie, but I've never seen any set dates on either court ruling for a specific time.
Has anyone else come across this information, and if so, do you have the source?
(Oh, and to give credit: the forum replier was user PixieBite. I would simply message this user for a source, but the profile hasn't been active in a while.)