Am I able to use the 144 hour visa-free transit? Thanks!

Hello there, I'm planning a trip following the next itinerary: Mexico-USA-Seoul-Shanghai-HK-USA-Mexico. The thing is that in USA and HK will have a layover on some hours but in Seoul I will be some days. In Shanghai I would like to be less than 5 Days ( around 120 hours). Strictly speaking, I'm not having a layover in Shanghai but want to be there and then return to my country via HK and USA.