We did a 2 hour with a 1 1/2 and 2 1/2 yo and it was perfect. I think and all day would be WAY too much for your little one not to mention the heat and the need for you to pack enough snacks and drinks, toys and whatever else for the whole day on a boat. I think 2 hours and you will see enough and enjoy yourself. All day and you might be stressed because of a tired, cranky 2 yo.