will I need a double entry Chinese visa? I have a UK passport.

Hi,
I am flying from Tokyo to Shenyang before heading into North Korea the next day (crossing at Dandong). I am then leaving NK a few days later and flying from Dalian to Seoul. On both occasions, I will be in China for less than 24 hours, and will be able to produce proof of my outbound flight from Dalian as well as my tour to NK by train. Am I eligible for the 24 or 72 hour transit and if so would I need to apply for two (one for entering China from Shenyang and one for the return journey to Dalian)?
Thank you in advance!