Well, a lot of the holidays we have here in reality mark important parts of the year.
Like Halloween, or All Hallow's Eve, or as it was known in Gaelic, Samhain (which is my favorite holiday), traditionally was the time of the harvest, and is called All Hallow's Eve because it's the evening before November 1st, All Hallow's Day, which is a Christian feast honoring the saints, whether they're named or unnamed.
Christmas comes from the pagan tradition Yule (which I celebrate), at least how it celebrate it in the West, which marks the winter solstice, and many traditions are around keeping nice, warm, and cozy, and feasting. It was then adopted by Christians to mark the birth of Christ, even if Christ Himself was born around mid to late September.
New Year's marks the new year, which, is itself more of a cultural thing than it is an astronomical thing, because the Earth does not revolve around the Sun every 365 days. It actually falls about 6 hours short of that, as it takes it around 365 days, 6 hours, and 9 minutes to revolve around the Sun.
Which is important, because you want a fairly consistent way to keep track of time so you know when it's appropriate to plant your crops, and when it's time to harvest them. You don't want things ass backwards by celebrating harvest day festivals in spring time.
So, you compensate by adding a day to the calendar every 4 years, which overshoots it a little, so every 100 years, we don't do a leap year, and if that year is divisible by 100 but not 400.
Which realistically means that the years, 2100, 2200, and 2300 will not be leap years, but 2400 will be.
Why do we do this?
Because we're prioritizing the day because it's convenient for us for several reasons. The astronomical way to do it would be to mark Earth's position in its orbit, then celebrate the New Year when it reaches that exact spot in its orbit again, which becomes less of a day, and more of a moment to celebrate.
Easter is tied to Judeo-Christian traditions, and traditionally is celebrated the first Sunday after the Passover, and is the time to celebrate Christ's Resurrection.
Lent is the days approaching Easter, is a time of fasting, prayer, and such.
Independence Day is on July 4th, and we Americans know what that marks.
So holidays are marked if they're significant in a social, cultural, political, or religious context.
So I'd imagine Hyrule would want to mark the date of their founding (which we don't know what day that is); they'd want to mark the time of year when to harvest crops (which is around autumn/fall); it'd want to mark the New Year; it'd want to mark religiously important moments; and to celebrate moments that are culturally significant, like, every year, around this time, a certain natural phenomena happens that brings people good fortune and luck.
Holidays are an interesting way to look into the values that people hold, and it shows us that many things about Hyrule we simply do not know.
Current ones I can think of are the Carnival of Time, the Picori Festival, and the Wing Ceremony.
