Question re VISA exemption travelling by train

Hello,
I am flying from London to Guangzhou on 19th May. I have a single-entry tourist L type. I leave Guangzhou on Saturday 27th May. My flight is to Jakarta, Indonesia.
Now, I am considering visiting Hong Kong on Thursday 25th. As I do not have double entries and quite tight to apply for it before I fly to China, I am considering other options.
If I take a train back from HK to Guangzhou on Friday 26th, would I be eligible for a 24-hour direct transit if I fly from Guangzhou airport the next day? Do they grant those at railway stations?
Many thanks for your help!