why is the Pl. Gen used here? i thought V needs the accusative thus V koliky hodiny?
Disclaimer: I am learning, too, so you may get a better explanation from someone else. Meanwhile...
Here "v" does take the accusative form of "kolik." which is... "kolik." But then "kolik" takes the genitive plural when the noun that follows it is countable, so you get "hodin." Hope this helps!