Could you change the timing of the catamaran to a later time? In that way you could take an early ship's tour starting at the ferry port, take a taxi to catamaran port (Vlyhada?), and get dropped off at the tender port at the end. I know there are lots of ifs and wishful thinking, but maybe you can make it work.
Seabourn.
Google 3D excursions Greece. There is a company that provides the equipment and IIRC they list tour companies that use it.
Also google Olympia excursions, some providers might list them.
Combined tickets are valid for 5 days. You can start at any of the sites, but must visit the rest, in any order, within 5 days of first use. So, yes, you can visit the other sites the day before your timed entry to the Acropolis.
A taxi is the surest way to arrive at the main entrance for the earliest possible admission. It is worth a little splurge. You can use public transport the rest of the day when you are not pressed for time.
Just saying. A one way flight from Athens to Santorini in the first week of October starts at 45€. It takes 25 minutes. If at all possible, consider going to Santorini for a day or two before or after the cruise. No donkeys, no cable cars, no six ships in port.