I use frozen with my boa and hognose. With the rabbits that are 2lbs or so, I let them sit in the fridge for 2 days to thaw and then stick them in the bathtub until they are warmed through(this may take 30 minutes or so depending on how frozen the rabbit is still). If I had rats for her, I would take out however many I needed, stick them in the fridge(in the sealed bags) and leave them for the day or 24 hours, and then stick them in a large pot filled with warm water for 25-30 minutes to make sure nothing is left frozen. The pot I use has a big convex glass lid, so I just flip it upside down so the rats are fully submerged.

With the hognose's large fuzzy/small hopper mice, I put them in a sealed baggie, put some lukewarm water in a cup in the sink, stick the mouse in, and put another water-filled cup on top of that so everything is submerged. After it has thawed, I run some hot tap water over it until it has been warmed all the way through, and then feed the snake.

When I was feeding my one Ball Python(Amani, when I had only one) frozen mice, if they heated up too quickly or stayed too hot for too long, the belly would burst.

If I had to do that with the 40 Ball Pythons, I would be feeding for 6+ hours, LOL.