It looks like you're right.

I'm the author of this kata, and I know that someone else edited my test cases, so apparently they let a mistake pass through. I originally had many, many test cases (one for every minute of the day, in fact), but none of them had a 0 for the hour.

Thanks for bringing this to my attention.

Edit (2020-06-10): I reverted the tests so that they now handle ALL cases once again. That is, every single case is tested -- all 1440 of them.