You are right, especially regarding this one: https://www.codewars.com/kata/578fe7e2149935740f000525
I tried hard finding similar ones before posting.

I would appreciate if you could tell me if there's a way to detect that illegal code was used (Linq's OrderBy, other array sorting).

Shouldn't the MaxTime be sufficient to detect this such less performant code ?

Fixed it.

Took care of 3 points you raised.

Changed the requirement to "at least 60%" to avoid ambiguity.

All these character counting are at higher level.
Even the simplest one, ranked at 8sku relies on some data structures (other than just a string, bool)

Thanks for bringing forward these examples, but these demonstrate my point as they require a function that gets a list or an array...This requires more knowledge. The return value is also not just boolean.
Nevertheless, I'll avoid authoring for now. It seems what I'm doing is not as useful as I thought it is.

It says 51% so 51%. Maybe I should make it 55% or 70% to make the intention clearer.

As for authoring and inspiration - I'm not looking for inspiration. I'm looking for a way to bridge an existing gap between the existing CodeWars Katas, and the typical new student who is just learning to program.
During the summer I took a few days to ramp up my score, for the purpose of being able to author, so that I connect my students to this site, and be able to add questions I'm missing.
I think my initiative should be welcome.

You look at this from a programer pespective. Please look at it from a teaching perspective.
For kids who just start learning, this could be one of the first times they write a function.
It could be the first ever for each loop, before learning about arrays.
It could be the first time they handle correctly integer / non integer arithmetic.
Maybe it's one of the first times they increment counters.

I think there should be a "9" level added, for the questions that are considered too easy...
It's one of the things that bother me about codewars. A highschool student cannot start solving (almost all) questions until he has knowledge of:

1. Conditions,
2. Loops,
3. Functions,
4. Arrays,

If you find the duplicate please send a link here. I searched and couldn't find one, and I searched quite a bit.

Fixed

Sorry. Updated description.

Added random tests.

I flipped the values so that reported test errors are now more appropriate.
I would appreciate an example of how to randomize tests
Specificaly, I'd like to know how can I send random input to my solution (so I can generate the "expected result") and call the user's code for comparison.
Any other example of random testing would be appreciated.

The questions are indeed similar but the referenced duplicate has a different signature (string parameter, instead of int). Input lenght and ways to handle it in the code are therefore different.
The current question is aimed at practicing / and % (as opposed to handling substrings and possibly conversions).

Fixed this. My initial understanding of AM PM was incomplete.