[12345hn6789]

It is quite odd to call this advent when it ends halfway into the month rather than on Christmas. But I will have fun doing them either way

[smokel]

It may have made more sense to start on Christmas Day, matching the Twelve Days of Christmas [1].

[1] https://en.wikipedia.org/wiki/Twelve_Days_of_Christmas

[tgv]

I think there's a problem every other day, so it's 1, 3, ..., 23.

[alexfoo]

No, the puzzles are every day from the 1st to the 12th inclusive.

From https://adventofcode.com/2025/about:

" Why did the number of days per event change? It takes a ton of my free time every year to run Advent of Code, and building the puzzles accounts for the majority of that time. After keeping a consistent schedule for ten years(!), I needed a change. The puzzles still start on December 1st so that the day numbers make sense (Day 1 = Dec 1), and puzzles come out every day (ending mid-December). "