Give yourself some time to visit the various places around the region including a couple of days at Fraser Island and a night at Lady Elliot Island (located on the Great Barrier Reef). The easiest way to see Fraser Island is on a tour (1,2 or 3 day) however there is the option to hire a 4WD and drive yourself if you confident driving on sand and wish to take your time.
If you are planning to go whale watching the best time to travel is from July to early November.
Hervey Bay is a great place to base yourself, then you can do short day trips up and down the coast, visit wineries & hinterland or out to the islands.
Swimming is good all year round as the waters in Hervey Bay are protected by the surrounding islands.