My experience at POR and POFQ was, you could go in 24 hours, as long as you were quiet. I took a walk at POFQ after 2am (too excited about WDW). I struck up a conversation with a security guard hanging around the pool area. We both quietly watched a father and his child in the pool. As PP stated, lifeguards go off duty at a certain point. After that you're on your own.
I had problems years ago with my young DD. I sat in a lounge chair and she would be in the pool alone. It was way past bedtime but she wouldn't get out, and wouldn't come to the edge so I could pull her out. We would have stand-offs until DD got completely cold and tired, which was long after I pooped out. Where do kids get their energy?