Well Hongkong is a transfer destination for many people. WIth a 10 hour layover, you would probably have 7 hours to do your own thing. You can join a tour, but many of the sights in Hong Kong are in a local area. Eg, take the train or bus into Tsim Tsha Shui and walk along the foreshore there, maybe walk up to Moncok and Temple street for some market shopping. You can take a ferry across to Hong Kong Island and either take the cable car or walk up Mt victoria. Depending on the time, eat some Yum Cha, or queue for 2 hours to eat in the world's cheapest Michellin starred restaurant. You are also on Lantau island anyway, so you can go up the mountain there to see the big buddha. Remember give yourself plenty of time to get back to the airport. Also it will be warm, you biggest problem is you will nice and sweaty when you get onboard your flight.