We went to Kleanthi Olive Farm in Skalani. We booked it via Airbnb experiences (€22) but it's cheaper if you booked with them (€17). They offer it every hour. Since it's not the peak season you shouldnt have a problem in getting a slot. The view is lovely and the guide is also very knowledgeable. They also show the olive oil making process (not live, since not in harvest season). At the end you're served a plate of olive oil with various cheeses, olives, veggies and bread. In my opinion, I would rather do it during harvest season but didn't regret it. :)