Please help, my flight will reach HKIA at 18:00..can we go directly to guangzhou? how?

Hello, I'm planning to go to Guangzhou from hongkong. My flight will reach Hong Kong at 18:00 on June 18....will we still be able to catch up the train to Guangzhou directly from Hong kong Int'L airport? What time is the last train to Guangzhou east? do we have to go thru the immigration of hong kong first to take the train? And how we go to train station which leading to Guangzhou? How long will it take from hongkong to Guangzhou?

Please kindly email me back as soon as possible because i really need this kind of information. Thank you very much