Take airport express train to Central - buy return ticket.

Buy/charge Octopus Card.

Go to Pacific Coffee and use free internet.

Go up the Peak on Peak Tram.

Take a look around Soho/Mid Levels around the escalator.

Go to Ap Lei Chau if you can, take the double decker trams and a sampan/taxi if you need to, or bus (90B or 91).

Eat some lunch.

Go back to Central - take MTR to Mong Kok.

Walk to Tsim Sha Tsui / The Harbor from there

Take Star Ferry to Island.

Pacific Coffee/Starbucks.

Repeat/Go to your favorite place if you still have time.