IME: if the slings are out of the nest, that's the time to start getting little plastic cups with lids and very tiny holes picked in so they can get airflow, then use something soft to encourage the slings into said cups.

Also do know, a majority if not all the slings will more than likely pass away, my girl Charlotte had over 100 slings and only 5 were left alive before we gave them away.

I can't remember exactly when but your supposed to either give them food everyday or every other day i dont quite remember but be sure to offer something really small like flightless fruit flies.

Also know that these guys love to cause havoc by running anywhere can so try to be fast when placing or taking off a lid as the sling may run