These swift ships depart promptly, and on two occasions that I experienced, a little bit ahead of schedule. Be there at least 30 minutes ahead of time, and make reservations in advance when possible. In the event of rough weather, the hydrofoils may be cancelled. If you are travelling Greece with luggage, the hydrofoils are minimally accomodating. Expect to handle your own bags.
Crowded voyages mean baggage stuffed in every corner, another hazard if the trip is a little rough.
For those prone to seasickness, be aware that these journeys are not always glass-smooth, at least on the smaller hydrofoils. Rough water will make itself felt. You may want to avoid sitting in the forward cabin of the vessel on the yellow Ceres vessels, particularly during late spring, early autumn, and whenever storms are in the area. Stay inside the broad, flat rear cabin. The outside areas of the hydrofoil are very tempting if you have a still or video camera, but once the ship hits full speed, you may be at risk if you are outside.