Melbourne in 2 Days with a Car Hire?

My family of 3, including myself, are looking at a car hire in Melbourne for a day or two, but we're unsure of what to do. Here is our plan thus far: we are planning on staying in Melbourne for 3 nights, arriving very late the first day, so really we have 2 full days in the Melbourne area. But instead of staying in Melbourne, we would like to take a day to drive the Great Ocean Road from Melbourne to the 12 Apostles near Port Campbell, and back. Additionally (if time allows), we would like to see the Penguin Parade on Phillip Island too. We're thinking of staying in Melbourne for the first half a day or so on the first day, then renting a car to drive to Philip Island for the evening Penguin Parade, then coming back to Melbourne for the night, and then driving the Great Ocean Road the following day. Would this be a do-able itinerary? If we were to see the Penguin Parade, what time should we leave Melbourne to see the penguins if the sunset is at around 5:15 pm? Otherwise, we could pass on the penguins and just see the Great Ocean Road and the 12 Apostles, but we would like to see both if possible. What are some suggestions, thoughts, etc.?