Fish out of water

Hello. I've been curious about this for a while and wondered how long Ariel and the other merfolk could stay out of the sea? They are half human and the movie shows Ariel on the beach or on a rock for what seems to be a while. She didn't show signs of breathlessness either. Perhaps Ariel, who's curiosity has led her to crawl on land for long periods, had developed a stronger set of lungs/gills than her family. I'm also thinking of the TV series as an example. What do you guys think?