Mexican in transit in Guangzhou

Hello, I'm Mexican and will be traveling to Thailand and returning from Singapore, next November, via air like this:

Mexico city - Vancouver - Guangzhou - Bangkok (transit in China is 5 hrs 45 min)
Singapore - Guangzhou - Vancouver - Mexico City (transit in China is 7 hrs 20 min)

I thought I should use the 72 transit free visa, but after reading, I think I am ellegible for the 24 direct transit. Am I right? If yes, do I need to arrive to the airport with any special format? Or just the format that one gets on arrival to China?
Thanks in advance! :-)