I recently had to cull a feeder rat that was getting too big for a snake that is on a hunger strike. Well now I have a frozen rat that I dont really intend you use anytime soon. I feed my snakes live but its nice to have that rat as a back up in case that i cant go to the store for a while (Chicago weather). I was thinking of buying just a few more but only as a backup. How long can I keep frozen feeders?