How long should a dog be kept outside in cold temperatures and snow?

If a person ties a dog outside during the day, how long would be safe for the dog, a german shepherd, to be kept out there in 24 degree weather and with no dog house or shelter. What if all he has to lay on is snow?
Update: I totally agree guys. Here's the thing, its not just one person, but more like an entire county. It's everywhere you look there and I find it absolutely despicable.
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