The Daggerfall Chronicles lists Chil'a as taking place on the 24th of Evening Star.
The region of the Iliac Bay has a rich history, and not surprisingly, a number of holidays unique to it because of this history. The Breton and the Redguard cultures have many similarities, but just as many distinctions. An analysis of the holidays is one way to study the people.
As any schoolchild could tell you, the Redguards are a relatively new culture to Tamriel. Their arrival from their homeland is actually well recorded, though it occured several thousand years ago, in the 808th year of the 1st Era. Hammerfell was a great desert encompassed by almost impassable mountains -- unclaimed and unwanted. Many of the holidays extant in modern Hammerfell seem to be direct translations of older Redguard festivals before their migration to Tamriel.
The orgiastic seasonal celebrations seem unusual in a province with few changes in the weather from month to month. Yet on the 28th of Suns Dawn, the Redguards of the Banthan jungle celebrate Aduros Nau to relieve the wintertide lethargy; on the 1st of Mid Year, the people of Abibon-Gora celebrate Drigh R'Zimb in honor of the sun, which no normal Redguard worships in this day; similarly, on the 29th of Suns Height, the festival in the Desert called Fiery Night, seems almost perverse in such an environment; the Koomu Alezer'i on the 11th of Last Seed in Sentinel has been translated as a harvest thanksgiving, though many scholars have suggested that it was once a springtide holiday; similarly, the Feast of the Tiger in the Bantha on the 14th of Last Seed was probably once a religious holiday to a Tiger God, instead of a thanksgiving.
Other old Redguard holidays have either been acknowledged as part of the old culture or adjusted to fit with the climate of Hammerfell. The Serpent's Dance, for example, of Satakalaam is patently an old festival honoring a Serpent God of the homeland who evidently did not survive the journey to Hammerfell. The significance of the date, the 3rd of Suns Dusk, has been lost with the Serpent Priests. Baranth Do, on the 18th of Evening Star, and Chil'a, on the 24th of the same month, are both New Years festivals. Most likely, they have been moved from their original dates to correspond with the notion of the year defined in Tamriel.
The Bretons have been in Tamriel since before recorded history. Their holidays have remained almost unchanged since primitive times, though new holidays have been created to replace those which have lost popularity.
The oldest holidays still observed in High Rock must include Waking Day, on the 18th of Morning Star, when the people of the Yeorth Burrowland wake the spirits of nature after the winter, very nearly in the tradition of their more reverential ancestors. Flower Day, held on the 25th of First Seed in the smaller villages of High Rock is most likely just as older or older. The old cult of the flower is also remembered as Gardtide in Tamarilyn Point on the 1st of Rains Hand. Daggerfall's Day of the Dead, on the 13th of Rains Hand, suggests the ancestor worship that marked the Breton religion of antiquity. Finally, the ancient goddess of the moons, Secunda, is remembered in the Moon Festival in Glenumbra Moors on the 8th of Suns Dusk, just as the nights begin to grow longer.
The more recently created holidays of High Rock are those like Tibedetha, "Tibers Day," celebrated every 24th of Mid Year in honor of Alcaire's most famous, son, Tiber Septim. Likewise, Othroktide on the 5th of Suns Dawn is held in honor of the first and most illustrious Baron of Dwynnen. In quite extreme contrast, Marukh's Day on the 9th of Second Seed, is a solemn holiday, immortalizing the lessons of the equally solemn 1st Era prophet Marukh. My favorite of the modern Breton festivals has to be Mad Pelagius, held in mock honor of the most eccentric of the Septim Emperors. Pelagius was, after all, a prince of Wayrest before he became King of Solitude, and then Emperor of Tamriel. The Bretons like to boast that it was his time in High Rock that drove him mad.