Last direct coach from HKG to Guangzhou departs at 10:15p. You'll miss it. So, you have to make a connection. Forget Shenzhen Bay as last coach departs 10:20p. So, just take a coach to Huangguang, cross the border, and then look for coaches to Guangzhou. I don't know specifics, but there should be coaches 24 hours. Whether you can get to GZ by 2am is unclear.