Hong Kong to Guangzhou Station and return. Where di I buy tickets where do I find time table Thanks

As far as I know, there are two companies operation cross-border buses between GZ and HK. They are Chinalink Bus Company Limited and Trans-lsland Limousine Service Limited Company and you can find the detail information on their websites and book the tickets online in advance.
Generally speaking, the buses stop in Garden Hotel, Guangzhou Hotel, China Hotel and so on in Canton.