Train Transit HK-Laos

Hi, I am thinking about the following itinerary by train, as the rules also seem to allow 24h train transit. Does anyone know if I can get a 24h exemption at Hong Kong West Kowloon Station? Of course, I would have all tickets ready to show in Hong Kong.

G6542 HK West - Guangzhou South 15:08-16:19
G2922 Guangzhou South - Kunming South 16:48 - 23:30
D887 Kunming South - Vientiane 08:08 - (depart last station in China, Mohan, at 13:23)

It is my understanding that this is less than 24hrs in China, so should be permissible. Has anyone actually succeeded in doing a similar itinerary?