More like 2 months for canines. But you could allow any female form to do too.
You caught me in a stealth edit. I had originally written "he'd be stuck in the form of a horse for nearly a year!" Thinking about what actually happened to Loki. Then I remembered we were talking about Hati...
Yeah.
The other day I came across this from the old WotC Fey Feature web articles:
https://www.wizards.com/default.asp?x=dnd/fey/20030214aWhile the Seelie Court celebrates the turning of the seasons, the Unseelie Court chooses the phases of the Moon as the focus of its merry-making. Much more comfortable with the shadows of the night, they feel a special kinship with the cold and harsh lunar mistress. These celebrations are sometimes a parody of the pomp and elegance of the Seelie Court, sometimes homage to their own twisted states of being, and at all times a chance to enjoy the misery of unfortunate "honored guests."
....
Ceremony of the Dark Moon
The Ceremony of the Dark Moon is held every four hundred and thirteenth year. The 41-day event is the most highly regarded by the Unseelie Court, for during this time two important astrological phenomenon occur simultaneously.
First, the comet Sharani Kel appears. Its orbit brings it close enough to be seen in both the day and night sky for forty days. Lying low on the horizon, its trailing asteroids and galactic dust create the effect of a red claw ripping a gash in the fabric of the universe.
During this event, the fey druids offer sacrifices of rare creatures, one for each of the elements (fire, water, earth and air) each day, thanking the deities for the fey's long life and health. The ceremony takes place at the ruins in the center of a large crater. The fey believe that the crater, caused by a bolt from the sky that destroyed the stone dwellings of an ancient religious order that had fallen into apostasy, was a warning from the deities against forgetting who granted the fey their powers. Each member of the fey is expected to bring a memento that is valuable to him or her, and cast it into the fire at the center of the ruins.
On the last day of the ceremony, the moon travels in front of the sun, causing the land to grow dark around midday for about an hour. During this time, parents bring their offspring to be blessed by the chief druid. As faerie births are rare, even among the less discriminating fey of the Unseelie Court, there are generally no more than seven children brought forward. Each child receives a small vial of blackest night on a leather cord. This vial, when opened, causes the land to darken while still allowing the wearer sight.
Vial of Blackest Night: Once per day, speaking a command word causes this vial to activate a deeper darkness effect that functions per the spell, except the vial has no effect upon its holder's vision. Only one person at a time can hold a vial and gain the benefits of seeing through the spell. The vial does not grant the ability to see through other deeper darkness spells.
Caster Level: 5th; Prerequisites: Craft Wondrous Item, darkvision, deeper darkness; Market Price: 5,000 gp; Weight: --.
I've got to make use of that mentioned solar eclipse... even though it would be happening at night on Vanaheim (with my planar set up, there is no possible way for the Unseelie Court to be doing anything during the "day" on Vanaheim).
The comet is "low on the Horizon," so if I just say that it is low on the horizon in the south, then it's always been there, just off-screen (as my players are all in the far north), below the horizon from my players' perspectives.
The only "problem" with it is the description doesn't take into account the flowing time of the Faerie Realm. Forty-one days every 413 years... on the material plane? Or in the Faerie Realm?
At my flowing time rate of ~29.5 days Midgard = 1 day Vanaheim, that's a pretty big difference.
If it is every 413 years on Midgard, then it's every 14 years in Vanaheim.
If it is every 413 years on Vanaheim*... then it's every 12,195 years on Midgard...
*One thing I've not made up my mind about yet is how the seasons on Midgard interact with the days and seasons on Vanaheim. On Vanaheim, are summer and winter a mere 6 days apart? Are the seasons on Vanaheim completely divorced from the seasons on Midgard (I think this is the route I'll go).