Realistically, you should put it down and freeze it if it doesn't get eaten within a day. At that age they still rely on the mother for most of their needs, and keeping it alive is kind of cruel when it needs mom for warmth, and food. Essentially what you're asking, and I mean it in a realistic way, not trying to be rude, is 'how long does it take rat pups to starve to death?'.



I would recommend putting it down, freezing, and trying again another day.