I'm not too knowledge on roach-feeding to T's but I'm not sure if it's safe for slings. I know certain roaches(hissers/dubias?) should only be fed to large T's since their fangs are strong enough to pierce the exoskeleton and any smaller T's could damage their fangs. As for feeding, You should try and see if their fangs are completely black before attempting to feed. For slings that usually takes about 5-7 maybe 10 days. Any sooner and they could still be soft and you risk damaging their fangs.