Yes, as you said the whole sales markets will be closed about six a clock, in that case you can take the subway line two to Gongyuanqian and interchange to line one to Huangsha to go to the Shangxiajiu Road pedestrians street to have a sightsee at the night market and pick up something new there, of course that place is not a whole sales market, but you can buy some thing at a cheaper price than the whole sales market.
Oh yes maybe you plan to buy the croc shoes, because many guests from Malaysia, Brunei and Indonesia have bought the croc shoes just near the Guangzhou railway station, behind the Wantong hotel. That place is not far from the Liuhua hotel, you can go there on foot and it will be opened until eight thirty.
Good luck!