no hints

That's impossible, 366/7 < 53

I'm confused because inevitably there are several days that occur 61 times in a year, but there are test cases that expect a single day. I assume I'm misunderstanding the kata's desired output, though. Can someone better explain what exactly this thing wants?

Let's say this kata is reranked to 7 kyu, then I could complain about there are harder 7 kyu katas than this one, so? The problem is you're expecting all 8 kyu katas to teach you fundamentals and this is a puzzle kata. You either like it or not, to each, their own.

And rightfully a 61% satisfaction rate

Ranks can't be changed anymore, so... here we are, with an 8 kyu rank and a red warning.

8kyu about addition and multiplication are essentially formuals as well, let alone 8kyu Katas with regex, so that's not an excuse. But you get the point, you can think of a solution as simple as possible to most Katas of any rank, so it should be the amount of effort that determines the rank. This one since it claims it's more difficult than other 8kyu katas then by definition it should be 7kyu. The 8kyu is deceiving for starters

But there are many examples of Katas where the solution is trivial as well but due to the mind effort you have to put the rank is higher than 8kyu. Such as https://www.codewars.com/kata/55fd2d567d94ac3bc9000064
And furthermore, this one doesn't represent a real world problem. The list is specifically designed to require a solution like this, as well as the rules. The point is such thinking is not a skill you have to improve, it's for amusement.

I'm not trying to be a snob or anything, but yea, this Kata was very funny and stuff but it's... kind of opposite of what codewars is about, to practice programming and to improve your way of thinking and problem solving skills. This teaches you nothing. Also, 8kyu Katas' purpose is to be an introduction, which this one also fails to fulfill.

You learn to think before you code. Seems reasonable to me.