What is the minimum time required to visit Hong Kong Ocean Park, excluding the rides?

Well, you are suggested to have 5 to 6 hours to tour around the park (not include the riding time).
About the transportation, you can take public bus no.171 from Man Ming Lane, Nathan Road, and get off at Aberdeen Tunnel Toll Plaza. It takes around half an hour. And the ticket fare is 11.1 HKD per person. After arriving, walk south around 280 yards to find the park.