We are planning to get the Hellenic Seaways fast ferry from Piraeus to Naxos on Sunday 27 June. We do not want to book tickets in advance in case our flight is delayed and we do not make it to Piraeus in time for the 16.30 sailing. Hellenic Seaways are being very unhelpful - they have advised us to go to prebook and go to their ticket office in Piraeus to collect tickets. However, they then state that their ticket office is CLOSED on Sundays! Is it essential that we prebook tickets at this time of year or can we take the chance of buying tickets on arrival?