There are no legal restrictions ... how long they can stay outside

That's not quite what the source (beware, unpleasant images) says;

No other requirements - such as ... the amount of time spent outdoors ... are specified

An animal that is allowed to go outside every day, but always chooses not to, satisfies the latter but not the former. Which is actually the case? Moreover, these are very morally distinct! People who are forced to stay in a cell are prisoners; people who choose to stay in a cell are recluses.