Reverse engineer a convention-breaking (C#) implicit interface. So pretty the opposite of what you would be lookign for in a kata.

I fixed that "00:00" time, and added "00:00" as valid time.

I think you're right, there wasn't any logic behind that constraint, I've added "00:00" as valid🙏

I've added "00:00" as valid🙏

NOTE: [We don't have "00:00" time]

But 00:00 is a real minute that exists within 24-hour time. Do you mean00:00 is expressed as 24:00 instead?

it's part of the twist

It's not funny. You should provide a real reason for that.

I've added "00:00" as valid🙏

Diasllowing 00:00 as a valid time is just an unecessary side-constraint (and the kata-description lacks clearness anyway).

Which line breaks should be there? What is wrong with variable names "a" and "b"?

Because they do what they feel like.

Why do people think not naming variables or avoiding linebreaks that definitly should be there is a good practice?

Without any need you are expected to treat 0 as a special case as it lacks the spaces of all other non-negative inputs. That's pretty arbitrary and (if considered good) should at least be properly stated in the instructions.