Whenabouts

Occasionally I'll use the non-word "whenabouts" in day-to-day conversation. It doesn't really make sense to me that "whereabouts" is a word while whenabouts isn't. Whenabouts actually seems like it'd have a better case at being a real word than whereabouts does. Consider the following exchange:

Person #1: "Did you hear that Best Coast is playing a show in town tonight?"
Person #2: "Oh yeah? Whereabouts?"
Person #1: "At the Garrison."

No one would question the use of whereabouts there, but all Person #2 really needed to say was "where?" What's the point of the "abouts" in that instance? Best Coast isn't playing in the general vicinity of the Garrison -- she's playing at the Garrison. Now consider this conversation:

Person #1: "I think I'm gonna go to that house party tonight."
Person #2: "Oh yeah? Whenabouts?"
Person #1: "Ehh, maybe 10-ish."

In this case, Person #2 is actually asking for an approximation. "When?" is stronger, and implies that Person #1 is planning to arrive at exactly a certain hour. Given the lack of punctuality by most people I know, I feel like whenabouts could be an extremely useful word for a lot of people.