I'm getting the same error, execution times on the harder and hardest tests are 2ms, 5ms, 195ms and 257ms. Could this still be slow?

same here

This is a 4kyu so it is expectable to be somewhat hard. If you don't want to waste your time, maybe you should stick with white katas.

Your code doesn't pass the sample tests, it returns [] everywhere...

Don't raise issues because your code doesn' work and you want points. That's not an issue. You say the kata has a problem because your code passes everything except the "more challenging cases". My code passes them, as hundreds of other people, so what? You can ask a question, but please provide clear information, logs, code, etc. Raising an issue saying you desserve your points is just childish and pointless. Please read carefully the documentation: https://docs.codewars.com/training/troubleshooting/

Your code has an issue, not the kata. Random tests are random. Read the documentation to debug your code (see left panel).