I don't know if I heard that somewhere or just made it up, but it is TRUE. I was walking a dog in 16°F weather today (real feel of 2°F), and was thinking about how much my cheeks were burning. I can only imagine how cold the pavement was for the little Sheltie (Shetland Sheepdog) I was walking.
I should be thinking about her, since I am a professional pet sitter and that is my job. But do pet parents think like this? I don't know. Do you? I would like to know.
Many people assume that because a dog has fur, it can withstand cold temperatures and cannot handle the heat. This is not completely accurate. When it is cold, think of your short-haired dog as a human wearing two layer of clothes. Would you be out in 30° weather for long dressed like that? Some people say yes, and some people say no. It is the same with dogs. Think of your double-coated furry friend as having good warm clothes on with a coat on top. How long would you be out now? I know some people who would be outside for hours because they would be active. I know others that wouldn't last 15 minutes because they cannot ever get warm.
The important thing is to watch your dog to find out what works best for it. If your heavily furred Saint Bernard is basking for an hour in the baking sun in 80° weather, that is probably too long, even if it doesn't realize it. If your dog is panting, it doesn't need a drink. This is how dogs cool themselves, so it is TOO hot. However, if your little Sheltie is laying on sun-warmed concrete on a 16° day for 15 minutes and she doesn't want to come in when you call, you can probably leave her for a little while longer.
I am not a veterinarian, but I am trying to help you find a good balance. If you want more guidance on this topic, please contact your veterinarian.