I found this on data for stackoverflow and just copied and removed tag grouping... gives 42min. average with a VERY high std. dev... doesn't really says much.
Of course, this may not be very precise, since many answered questions never get best answer selected.
And my observations says that the higher your reputation, the quicker an answer comes. hahahaha
EDIT: I should probably point out that I really don't believe these statistics! I looked for it just for fun. There are many things to consider if you're not getting answers here, that this simple query couldn't possibly consider: is your question well-written? Is it about a widely used tool/feature or something that nobody else even know it exists? Does it intrigues the reader (if your questions demonstrates you've tried everything the reader would have considered, he might be compelled to do some research too)? etc.