Hi, I am in Guangzhou and would like to go to Hong Kong for a 1 day visit, is this possible?

I have been granted a 1 entry Mainland China and entered through Guangzhou airport and would be catching the train to Hong Kong then returning the same day. My ticket out of China then leaves the next day from Guangzhou, is there any way that this can be done? Does the 72 hour visa free stay work for this?