A question for dog owners. UPDATED.

My wife and I have just moved into our New home and we have a large fenced in yard for our three dogs. Previously we did not have a fenced in yard and whenever we took the dogs out one of us just had to stay out with them to watch because we are rather close to the road. My question is, how long is it okay to leave your dog outside in the winter? We live in upstate New York, and I'm not talking about leaving them out for hours at a time. We love our dogs with us and they stay inside for a lot of the time except when they get exercise. But I'm just worried that if my dogs are hanging outside for little too long they'll get cold. They love playing outside and will stay as long as I let them, sounds silly but I'm generally curious what do you all think. For the last couple days I've been letting them out for about 30 to 45 minutes at a time, it hasn't been particularly cold and there isn't really any snow on the ground. Any thoughts or suggestions would be greatly appreciated thanks a lot!

Here's a link showing a picture of my puppies! http://www.democraticunderground.com/116114587

Thanks for the advice, folks! It seems I may have been premature in my concern. These dogs are in heaven, lol. They're very happy outside and it's been very relaxing playing fetch with them and not having to keep a sharp eye out for the occasional biker or runner we used to get.

And frankly the weather has been awesome! No white Christmas this year, we're looking at 40 degrees! Yay!!! Thanks again for offering up advice!