The ferry rides to the Islands are around 20 to 40 minutes depending on which island. The ferry piers are located in front of the IFC complex in Central. Time Tables are available at the individual piers, but generally there is a ferry twice an hour, more frequent at peak times. They run from six in the morning to late at night.
Is the largest of the Islands, has the largest Buddha outside of Thailand complete with its own Monastery. You can also take the cable car from Tung Chung, but check the website the day you plan to go, high winds can be a problem. The island also has some great walks, beaches and restaurants. Discovery Bay is very popular with expatriates with young families; it also has a very fast and efficient ferry service. Go to Silvermere Beach at Mui Wo on the other side of the Island, never busy even on public holidays, one of my personal favourites.
The next largest Island, but is considerably smaller than Lantau. It's unique in that it has no motor vehicles except an Ambulance and small Fire truck. Very popular with expatriates with young children, most of which go to school on Hong Kong Island. There are a number of sea foods restaurants, bars and local shops that cater for daily needs. Good beach, rolling hills, good for walks and keen mountain bikers. It does get very bust at the weekend as many visitors come over from Hong Kong for a day out.
Nice for a day out, very local, load of seafood restaurants and good value for money. Also has a good beach for wind surfing. Got some good walks but quite hilly.
Very small, very local. I went once, walked around it in about 20 minutes. No beach, one temple, one bar and a small supermarket, that's it. Had to wait nearly two hours for a ferry back to Hong Kong, not one of my better decisions.