I was at Plitvice recently and took my time. Arrived afternoon, saw lower falls. Path not strenuous at all, more walk. Can take boat (free, like little train), better walk whole path ~2.5 hrs.
Next morning hurried, at entrance at 8:00, to upper lakes more picturesque. Great, no crowds to highest lake 10:30. Back by train or foot. So if going, take time, beautiful, start early as possible. By 11am crowded.