Short on time? Saronic Gulf Three-Island Cruise (Hydra, Poros, Aegina) can wait.
Allow Full day (9–11 hours).
For a no-planning taste of the islands in one day it's efficient and sociable — buffet lunch, sun deck, three different harbours. The catch: it's the textbook tour-group experience: barely 60–90 minutes ashore per island, a packed boat, recorded commentary, and not nearly enough time to actually feel any one place.