As long as you're bundled up properly and dress appropriately for the cold and wear gloves, hats and coats it's okay to be out in the cold for at least 30 to 60 minutes at a time.
But in extreme cold you should avoid being out longer than 30 minutes because being out in the cold too long especially in extreme temperatures even when bundled up can cause your body temperature to drop which can lead to hypothermia.
If you body temperature drops below 95 F then hypothermia can set in and can cause death and if not wearing gloves you could get frostbite and even with gloves in extreme temperatures you can get frostbite then as well.
Also your feet and toes are also prone to frostbite because I got my toes frostbit before and it was painful even though I was wearing 2 layers of socks my feet got too cold and I had frostbite on my toes.