how long is from HK to guangzhou?

Hi, as for your case, the only choice for a direct journey should be take the direct cross-border coach to Canton at that time. The whole journey takes about 4h and the last cross-border coach departs from the airport at 22:15.

Or you can go to the nearby Skypier to take a ferry to Shenzhen in about 30min first. Then a taxi can take you to the local Train Station, where you can catch a bullet train to reach Canton within 1.5h.