Both are correct, there are usually two pronunciations; one of Chinese origin (the on reading) and one original Japanese (the kun reading.) Sometimes there are some rarer pronunciations too. Don't worry about that, you'll get used to it in time.
じ as in: いまは、なん時ですか。(as you already pointed out) 3時間。さん じ かん - 3 hours (time length) and others...
Postby community.japanese » December 1st, 2012 1:58 pm
public4889-san, エリックsan, That's right! Like Eric-san answered, both are correct readings. Thank you, Eric-san, for good advice!! I'd just want to add (you might learn later, or you might already know...) that ときどき is written as 時々; second kanji is a special one