Don't bother. Chances are, Apple Store HK will reuse the same reservation-pickup system they had during the release of the iPhone 4S and the iPad 3. No one will be able to queue up outside the Apple Store and purchase a device.
See:
http://micgadget.com/23550/apple-vs-...ew-ipad-video/
Other electronics stores like Fortress and Broadway may sell them first-come-first-serve, but you can bet on the queue already there one day in advance. There is no realistic way that you will be able to get anything on a 7 hour stopover.
Finally, that leaves the gray market resellers at Sintat and other shopping arcades. They will price the product sky high given how new Apple products always have high demand.