24 Hour TWOV

US Passport holder living in Seoul. If I fly from Seoul to Tokyo to Beijing to Hanoi to Seoul, and will only be in Beijing for under 24 hours, can I get the 24 hour TWOV? I read the 72 hour TWOV doesn't apply if you're staying under 24 hours.

I decided to book one way flights this trip, but I will bring all the printed receipts which have e-ticket numbers, flight confirmation numbers, and confirmed hotel bookings, too.

My main concern is if Seoul or Tokyo airline agents give me a hassle for trying to get thru China without a visa, and also if I get to China, I don't want to be confined to the airport because I have a hotel booking overnight.