Both questions are correct. But "Во сколько?" is used more often.

I think they're the same. In coloquial speech we use "во сколько".

в котором часу? referring only for hours, not specific time во сколько? this question requires specific answer: what hour and what minute you mean

Isn't "Cколько сейчас времени?" also correct?

Mostly we use "Во сколько?" when asking about accurate time. For example: "Во сколько пойдем в кино? (What time we'll go to the cinema?)" - "В 6.30. (At 6.30)" And we use "В котором часу?" when only jeneral timerange is needed. For example: "В котором часу он заканчивает работать? (What time he usually finishes his work?)" - " Около 7 часов. (About 7 o'clock)"