As native English speakers, what would "What hour is it ?" mean ? Exactly the same as "What time is it ?" ?? I'm not a native, but I've never heard such thing to ask the time...
So my guess is, "What hour is it ?" should be translated into "Quelle heure est-ce ?", which is slightly different than the expression "Quelle heure est-il ?".
In practice, "C'est quelle heure ?" (or "Quelle heure est-ce ?", more formal) can have answers such as : "C'est l'heure du cours de mathématique", "c'est la dernière heure", etc., i.e. referring to a time slot rather than the time the clock is showing...
Its like if you knew another language and were asked to translate, "She danced on the bar." You could translate it to mean, she danced on that long skinny rod looking thing usually made of metal, because it also means that. Its just more likely that that phrase is referring to a flat table looking thing, drinks are served on.
The words which elide (drop the ending vowel and replace it with an apostrophe) are: le, la, je, me, te, se, ne, que, jusque, puisque, quoique.
All of them end in a vowel sound (-uh or -a) This is why the elision helps pronunciation if the next word starts with a vowel sound as well.
"Quelle" is pronounced KEL, so the last sound is a consonant sound (-el) which does not trigger any conflict with a vowel sound.