well, you can contact CX and they should be able to assist you.

You will have time to go to the city and have a look, providing you use the airport express service. The train ride is 23 minutes from the airport to Hong Kong Island. If you travel by bus, it will take at least 70 minutes. Traffic is very heavy in Hong Kong, and you might not have enough time if you don't board the bus at least 2 - 2.5 hours before the departure.

http://www.mtr.com.hk/eng/train/ae_intro.htm

A tip for utilizing the airport express: Buy the SAME DAY RETURN ticket at the airport customer service center or choose the SAMR DAY RETUEN option on the ticket machines. This ticket will allow you to travel from the airport to the island for HKD 100.00/ USD 12.85 and your return journey from the island to the airport for free. All you need to do is keep the ticket after the journey from the airport to the island and insert the SAME ticket into the gate when returning from the island to the airport.

HKG is a 24-hour airport, and there are plenty of open space around. More info on HKG and its facilities: http://www.hongkongairport.com/eng/index.jsp