The only crossing you can use overnight IS Huanggang, and I don't think there's any direct coach from HKG to the border that late at night. You can take a green New Territories taxi to the transportation interchange just before Huanggang and switch to the 24-hour "Huang (Yellow) Bus" to the actual border; or you can go to various points in the city and use one of the 24-hour coaches to Huanggang.