Jeez, you'd think that all the doubles basses and other stringed instruments would have been destroyed by now if they exploded from 20 minutes of being out in the cold!
Hell, my CARVED bass traveled 5,000 KM this Christmas on a barely heated train in NORTHERN CANADA. If my bass can survive that, yours can survive a measly 20 minutes outside in Chicago. It had an open seam in the end, but who cares? This happens to every instrument, and I'd rather an open seam than a crack.
And if it cracks? So what? Wood instruments have been cracking since their beginning, and double basses from the 17th century still exist (all with loads of cracks). If a 300 year old violone can survive that long, I'm sure yours (and everyone's) bass can survive 20 minutes outside in the winter.
"What do you think happens after that note? Time stops? WHAT ARE YOU DOING?"