hi, we're planning a trip to athens and two islands in mid-april. my itinerary so far - 4 days in athens (including a day trip to delphi), 1night / 1.5 day in hydra, and 2 night/3 days in santorini. i've heard Fira and Oia are must-see in Santorini... do I have enough time? also, what is the best sequence and transportation to minimize travel time? thanks a bunch!