CZ's CAN-HAN flights leaves 1:05pm, while VN's HKG-HAN leaves 9:00am. So, if you really want to get to Hanoi earliest, you should fly Wuhan-Shenzhen, and then fly out of HKG the next morning.
Many direct bus services from SZX to Hong Kong proper. And the next morning, you can get to HKG easily from the city by Airport Express or Cityflyer Bus or taxi by 7am or so. Definitely no need to stay at the Regal Airport.