How would I access a ferry to Guangzhou from HKIA if the next one doesn't leave until the day after?

I am flying into Hong Kong at 18:00, and I see that the ferry only leaves at 09:30 and 15:30. I do not have any transportation plans set in stone beyond that point, but I would like to travel to Guangzhou and from there travel to Kunming. Would I be able to take the ferry, and if so, would I need to order those in advance, or could I just buy it when I get there? Also, since I would need to take the ferry the next day, would I need to leave the airport and find a hotel, or can I stay the night in the airport without having to go back through customs?