Hi Victor/ all.
Yes very very lucky for me & the fish!!
I too have lost a few cats amongst others in the past that have broke free including a large TSN, Sperator Ac, large fire Eel, Big Snakehead etc that have manged to find a way out of the aquaria.
I moved the HW from the Big Pond temporarily into a 36" x 18" x 18" underneath the brick piers of the 750G (UK) pond.
Still not sure how it got out as there is a large glass cover weighted down with half bricks.
I would hazard a guess of no longer than a few hrs but could have been as many as 3-4hrs but i seriously doubt it.
I can only think that maybe it got out throug the 25mm drilled hole on the side of the aquaria that was used previously for a protein skimmer but is only an inch or so above the water line.
I've now blocked this off as well.