on March 25 on the Shire calendar.

While Tolkien hated allegory, it seems he was nevertheless affected here by his Catholic religion, since March 25 is also the feast of the Annunciation, when Catholics believe Jesus began to be in the womb of Mary (b/c it is 9 months before Dec. 25). Either way, in RL and Middle Earth, the day indicated the beginning of the defeat of evil, and the reign of man (or son of man), as opposed to Sauron in ME, and the devil in RL.

I wish I had more original sources of Tolkien, so I could easily reference my comments here. History of ME would be nice, but I should probably start with getting the published volume of his letters. (Really, Eirikr, this is very unscholarly of you. And you call yourself a JRRT fan....)