As for snares, I've found them up by me with very very dead rabbits that have been there days or a fox has had them so snares are left unattended.
you check snares at least once every day for a number of reasons not just animal welfare, the longer something is in a snare the more chance a predator will beat you to it and you will have wasted your time if a fox has taken it from the snare, the point of snaring is to catch food for yourself not supply easy meat for other animals, and should you actually catch something in your snare you want the meat to be fresh not several days old, birds like magpies and crows will peck at the carcase, cats will chew on the carcase and badgers will eat the carcse too, incidentally you can always tell when a fox takes a snared rabbit because you will find just a rabbits head left behind in the snare with no body, when rabbits are snared they very often squeel and that attracts foxes to the rabbit which they will promptly eat.