If you buy a business class ticket on A3, you should get access to their lounge as well as getting flexibility to try to take the earlier flight. It's a nice little airline with good F&B as well as customer service.

With separate tickets (or even not) I wouldn't try the 55 minute connection, especially since flights to the Greek islands in high season can be fully booked. If you miss the early flight that you're booked on, there might not be available seats on later flights.