Too cold for mice??

[Classic]

Got a question....I've been keeping my breeding mice outside - because of the smell - and am wondering if anyone knows how cold is too cold for them.

I have 2 small tanks with 6-7 mice in each one and have had litters practically every day or two for the past 2 weeks. It's getting pretty cold overnight now and will hit the freezing point at any time. I had planned to put them all down when it got too cold. How much longer can I wait??

Thanks.