Harlan's Point is a great day or even half a day thing to do. The beach has a clothing mandatory and clothing optional area, so depends on your preferences. I would suggest purchasing tickets online so you don't have to wait in line when departing. There is not a great deal of shade, so wear sunscreen appropriately. Make certain you find out what time the last ferry departs to head back to Toronto, or else you will have to take a water taxi, which I have heard is not the greatest.