The idea of wanting a time seems odd. "I want lunchtime" or "I want December" or "I want ten o'clock"... it just sounds really un-idiomatic
I see your point, but it is a real sentence in English and can be used (however odd it sounds.)
"Mom, how many months until summer?"
"You must wait three more months."
"I want summer now!"
In your examples, "I want lunchtime" I agree it would make more sense for it to be "I wish it were lunchtime". But this sentence is what it is.
Well, I still disagree - I think the fact that you've had to use the example of (implicitly) a child's speech illustrates the point! It's not a sentence an adult would use. But it's not worth getting into a big argument about I guess :)