The Australian law is no more than ten minutes on a day over 28 Celsius.

That said for me it depends on the dog and how the dog is feeling right then. My dig is half Chihuahua, he’ll like on the concreted in the backyard on 40+ days when everyone is posting about how it’s dangerous for dogs to be out in the heat. I’ve known a bunch of kelpies - Australian working farm dogs - that are just fine in the heat as long as it’s not extreme.