In 2022 there was only one train departure time from Katakalo 8.40am (arrive Olympia 9.30am) and the return departure from Olympia at 13.10 hrs (1.10pm) arriving Katakalo 14.02 hrs. (2.02pm). Fare was €10 per person round trip.
There were private bus tours available at the port gate to Olympia, costs €15 per person, 30 minutes to the village, then 2 hours free time before returning to Katakalo. Bus driver /guides have excellent english. They wait until bus is full before departing, so no schedule as such and you may be waiting for a while at either end.
Also at the far end of Katakalo, adjacent to the train stop, is the Museum of Ancient Greek Technology. Really worth a visit.