You'd get 3 or 4 hours wandering around, train is about half an hour to Central. I'd do it if you haven't been to HK before, not sure if I'd bother otherwise. It's a nice enough airport to hang around at, particularly if you can use the lounge.
I can use the lounge, but I'd prefer to nip into HK never having been there before.
I can use the lounge, but I'd prefer to nip into HK never having been there before.