Hanoi - Nanning - Shanghai

Hi there! Thank you for a very helpful guide! I'm a bit confused as to whether I will be able to get a 144 hour transit. I'm currently travelling SE Asia but my flight home is from Shanghai. I'm hoping to get the train from Hanoi to Nanning and then onto Shanghai. I'll be in Nanning train station for something like 2 hours before boarding my next train. Will I be eligible for free transit in Shanghai? If not I'll have to get a very experience flight from Hanoi!