as stated, feed once its dark, and remove leftovers the next morning, ferrets dont tend to sleep all night, and the soon learn when feeding time is,
the jam jar idea is good, but of course you'll end up with a jar of maggots, easier idea is an empty coke/pepsi bottle, drill a small hole in lid, stick a couple of spoonfuls of honey in, diluted with around 1/4ltr of hot water, swiss it around and hang up on outside of cages/courts etc, you'll find it catches both flies and wasps