Originally Posted by
LHR/MEL/Europe FF
I had a problem with nested tickets at ICN, customs couldn't understand I needed to enter, check-in, and then depart again a couple hours later. Four officers came to question me and search my bags. Took about 30 minutes. Just a 'heads-up' that an immediate turn (in Korea) might be tight on timing if they decide they don't like your travel plans for whatever reason.
I'd just say I've to personally deliver item X (a letter or USB drive or whatever..) - or meet a friend for lunch/dinner/drinks, or anything. It's not really of their concern.. I've done more than plenty of those "6 hours in country" stunts all over the world, never getting more than a raised eyebrow for it - or in fact nothing at all. Also, I'd assume that this same day RT would be on the same ticket, you'd be protected should some South Koreans decide to go all crazy on you and you miss your checkin again.
That said, you probably could travel light on this flights anyway, leaving your bags in China in safety (either in the hotel, or at the airport left luggage counter etc.) so no need to get to a checkin counter after having done online-checkin already, and having a bit more time to spare.