Która godzina jest isn't right?
It should be OK, but the option with „jest” in the middle or just dropped completely is better.
Verb should be allowed in final position.
True, although the most natural way is to just drop the verb completely.
Wouldn't 'jaki jest czas' be correct too? My Polish family use that quite often too.
"Jaki mamy czas?" is also used. But the most common (and often) is "Która godzina?"
Dziekuje wam bardzo ;)
Hmm, maybe in some dialect or in colloquial use.
Why is it not 'Która jest godziną'? Would you not use the instrumental case here?
No. You only do that if you compare a noun with another noun. „Która” is not a noun.