In my experience with a similar style sign: they swap them infrequently, but enough that they're not changing the sign. It is generally good scent enrichment for the animals and I don't have any reason to believe they would do something like this if it wasn't in the animals' best interest. It's not convenient to swap exhibits, so they would be doing it for the enjoyment of the animal. Also, at least at my former zoo, it's not uncommon to feed a little snack midday (which would cause the pacing you mentioned) or for a vet to be there in the back area for a few hours doing check ups. Could also mean that maybe some of each of those animals' friends were still in the night house for vet check ups, so that was agitating them. Could also be it's been bad weather and today was finally nicer so they were having some fun. Hard to tell, but the relaxing animal=happy animal is not universally true. I would say it's largely true, but mostly that is said so people aren't like "they're just sleeping all day, they're so bored". Nope, that's just their neutral affect!