Get a reasonable expensive hotel either on the tip of Kowloon or on Hong Kong Island.
Take the airport express train (20-25 min, every 12 min) and then the free shuttle bus to the hotel.
You should be at the hotel around 70-80 min after your plane docks.

On the way back leave the hotel around 2:30 hours before the flight (to play it very safe). Take a cab (or the bus) to the closest train station (Kowloon or HK Island). You can check in there, train to the airport. This should give you at least 1 hour in the lounge for breakfast.

This will give you some time to look around and get a glimpse of the city.

Do a search here for hotel recommendations.