Translation:When will she come?
No, you don't "just use かのじょ for girlfriend." It's true that they say ガールフレンド as well, but it's both. For example, they would say (if translated directly), "This is my girlfriend," as 「こちらは私のかのじょ(彼女)です。」That would translate over to "This is my 'she,' (or girlfriend)" which doesn't really make sense. However, what everyone fails to realize and gets annoyed about is that JAPANESE DOESN'T DIRECTLY TRANSLATE TO ENGLISH!!! It's much more of an estimated guess of what they were trying to say... So, to restate the point, you're wrong. They use かのじょ for both the female pronoun and to talk about someone's girlfriend.
Itsu is "when" and nanji is "what time." Like, "what time is it?" as opposed to "when is x thing happening?" You could ask for the specific hour, I suppose, but both options are available, just like they are in English. A parent who wants grandchildren may ask his or her adult child, "When will you get married?" as opposed to "What hour will you get married at?" Things like that. I suppose "itsu" is just a lot more ambiguous than "nanji" while "nanji" is asking for specifics and kind of assumes the time in question is relatively soon/relates to a specific thing. (Like, "when will the band be playing?" when you're trying to plan when to get snacks or something. Things with a specific, set time.)
Of course, this is just how I understand it. If someone with more confidence has a better answer, go for it! I want to have an accurate understanding of how to speak this language, too. :)