Plan at least 4 days to drive around the island. You *could* drive around the entire island in 4-6 hours, but you would not be able to enjoy & take time to enjoy the beauty and true Aloha spirit if you were rushed. Purchase a book called "Hawaii - the Big Island Revealed". It's a WONDERFUL book that guides you around this breathtaking island. It gives you things to do, what highway markers to look for, and more.
Having a rental car can be a plus here, because it gives you an opportunity to explore the island on your own. You can purchase a map of the island at a local store or some are free at the airport or some hotels. It's not very difficult to follow. You can drive through and stop off at several beaches along the way, and take some great photos along your scenic drive. You can make it a half day or day long self guided tour! A map and other free brochures that are usually provided can help you decide where you can stop along the way.
Driving from Kona Airport there are all those black rock formation, and people write their names with small white stones
The big island is a great place to tour around. The landscape is quite varied from waterfalls and lush rain forests to cattle farms to lava flows and volcanic landscape...