Here's what I would most likely do

you land at 745AM, by the time you grab your bags and pass through immigration, i'm going to say its 815-830.... Find a place to stash your bags and bring a small backpack withyou consisting of the basics. i.e. tour book , camera, passport, wallet etc

830-900: Airport express into Central Station
9:00- 10:30 , Either have a breakfast at a local cafe (google Tsui Wah) , or have a early morning dim sum lunch at Maxims, which overlooks Victoria harbour. I reckon they are open by then?
10:30-12:00, Head up to the Peak by tram or by the Bus (Bus 15), its the most scenic part of HK. I'd recommend it for any first timer. there should be a easy 2km hike with great views.
12:00-15:00, depending on if you're hungry yet, you can always have lunch up by the peak or head back down to central. If not hungry, maybe a little shopping at IFC? Then i'd probably do more walking from HK Island towards the wanchai/causeway bay area.. just to get a feel of the city.
16:00-16:45 take a coffee break... my legs would probably be tired
17:00-1930 subway it over to Tsim Sha Tsui... HK should start to get dark by now and you should walk the avenue of stars to catch the famous HK Skyline. It's probably the nicest one in the world, and I say that without bias.
1900-1935- find something quick to eat
20:00- train it back to the airport via Kowloon Station, retrieve stashed bag, and hang out in the lounge.