So far, I've only seen reference to:

Ascension Mass---21st of Khadoven (Morrow)
Day of Markus---3rd of Trineus
Day of Doleth/Doleth's Day (?name isn't specified)---28th of Ashtoven ("End of Fall" is what the Five Fingers book says...which would make it the same as Giving Day, apparently)

Dark Ascension---14th of Doloven (Thamar)

Anybody seen any specifics on any of the other dates of import?