I pick up the car at the airport at 8 o'clock and drive to the Great Ocean Road. I arrange to stay in Apollo Bay on the first day, in Campbell on the second day, and return to the city center of Melbourne on the third day. Is this arrangement appropriate ?

This is basically everyone's arrangement to be of appropriate height.

Personally, I suggest that if you start early, you can stop along the Great Ocean Road and spend the night in Geelong, Lorne, Apollo Bay, and pass through those classic attractions. In the evening, arrive in Port Campbell for the night. It's a comfortable and leisurely 300-kilometer journey. Spending the night in Apollo Bay is a waste of time. The second day head north to the Grampians National Park and check in. The third day return to Melbourne in the afternoon.

We're also leaving for the Great Ocean Road on the 21st. Maybe we can get through. But I'm really envious that you were able to book a room in Apollo Bay.

Very leisurely, can go to the Blue Lake , it takes 5 hours to go back to Melbourne from the Blue Lake via the inland

There is no need to live in Campbell.