Need the wisdom of Sifnos lovers. We are arriving in Sifnos Sept. 6. Need to take the Sept.12 ferry to Paros. Should we buy those tickets in Athens airport on Sunday, Sept. 5 when we arrive in Greece or can we wait until we arrive on Sifnos Monday morning? I understand weekend ferries back to Athens can be crowded in Sept. and we need to get to Paros for a flight out to Athens after a 5 day visit in Naoussa. Many thanks for any advice.