Ferry service from HKIA to Guangzhou.

No. There is only one ferry scheduled at 11:15 that can take you to Guangzhou Nansha Port from HKIA.
Instead of that, you are suggested to take the direct long-distance bus. Many coaches at the airport still operate after 16:00. The schedules are from 16:25 to 22:45 at intervals of around 30 mins. It costs 220 to 250 HKD per person. The duration is 3.5 to 4 hours.