Guangzhou Baiyun Airport to South Railway Station after midnight or early morning.

Hello,
My flight have ETA at Baiyun airport around 2am and I have to take a train at south station around 7am. Please suggest how to travel this on time.

I known that subway will start 6am and I can't reach the train station on time. So, I'm searching the bus route that operate in night time. For example, this great searching tool tell me that, I have to take bus 866/866A to Garden hotel and transfer to South Station express bus, and many more routes. But I don't know the operation hour of those buses. Please guide me how to check the bus operation hour.
Best Regards,
Monsan