The line between Katakolon and Olympia operates about 45 minutes after the cruise ship arrives to the port.
The journey to Olympia takes about 30 minutes, and you have 2 hours to spent at Olympia, which are enough to visit the museum, the archaeological site and take a short walk at the souvenir shops of the village.
In any case, you will be at the port of Katakolon at least 30 minutes before the ship leaves.