Actually just went through this myself, and the community on Twitter told me it would take weeks after I set myself up to fail by telling Backers I would have their downloads ready in days. (Not knowing there was this approval process, and no indicator on how long it would take). I highly recommend some text on that page that just says "This can take more than a week for us to approve. Thanks for your patience." An average time would be great, but ANYTHING would be very helpful.