If you plan to travel from Serifos to Paros, the ferry will take 2 hours with a fast ferry. It could take up to 6 hours on certain ferries. In the high season of June to September, there are typically 8 ferry crossings per week. Paros does have an airport located south of the city of Parikia. Depending on your island hopping itinerary, it could be a good option to fly in and out.