72-hour Visa-free Transit or Direct Transit

We will travel from Rangoon to Paris on 10th January, with 8h stopover in Guangzhou Baiyun airport. We would like to visit Guangzhou for short sightseeing. We are from country enlisted for 72-hour free Transit, but can we chose 24h Direct Transit? What is the procedure for Direct Transit? In this case, do we need special permission/stamp, etc? Thanx for help.