We can't walk that far any more, either. There are no local buses that late. You can get the early bus at about 7am from Arillas to San Stef (on its way to Corfu Town) and it comes back mid afternoon. Maybe you could plan a meeting around that, the bus to Arillas in the afternoon and a taxi back. Wherever you go, the owners will gladly call you a taxi when you are ready. I don't know the cost but would guess 15 to 20 euros.
Hope this helps
Phil