Ferry is the best option if the timing match yours, otherwise I would take a taxi from HKG to the mainland border (entrance point would depend a lot of where is you meeting) and then get another taxi after the border to your final destination.

Taxi time all together shouldn't be more than 1h30min, 2h, crossing the border depends where you cross it but usually in the early hours traffic tend to be more china HKG than HKG China.

Good luck!