I believe it was a few minutes before the fish's keeper noticed it was missing, and yet another few before they thought to check the yard. But it landed in deep enough tank water to stay alive the whole time, and made a full recovery. Those large SA/CA cichlids are tough customers.
When I was thirteen, I accidentally left one of my white cloud mountain minnows in a water change bucket with just an inch or so of water in it for over twenty four hours. Incredibly, it survived.
I fancy myself a decent animal keeper... but anybody who's been doing it for more than a few years has more than a few embarrassing stories they'd like to forget. But it's better to live and learn than to start anew every day.