Hi, Hong Kong Ocean Park(https://www.travelchinaguide.com/attraction/hongkong/island/ocean_park.htm) opens from 10:00 to 18:00 on regular days. It indeed will extend the opening hours on some special days, but it depends on the park's plan and weather conditions, so to be on the safe side, you'd better leave the park before 18:00 and have a good trip!