Glad to hear you caught your flight in HK but sorry to hear your luggage did not make it, hope you didn`t have to wait too long to have it delivered to you.
After all our faffing about we changed our day of travel and have booked with Cathay after all as VN don`t fly on Tuesdays. We fly out of Beijing at 10am arrive 14.05 HK then 4 hours in HK and a later flight to Da Nang at 18.15pm (so hopefully that is plenty of time even with a delay) All flights booked now for our 3 week trip so fingers crossed the plan works.
Thank you all once again for your help and great advice, as if I had gone with the really short layover I would have been really worried.... 4 hours to enjoy the Business Lounges :-)