Sunlight (both time of day and sky condition), wind, and humidity are factors. The coat and condition of the dog is also a huge factor. My vizslas are in decent good shape and have typically short hair, but my friend's Griff had a coat typical for that breed and does not get the exercise mine do.
It was probably 70 when we started chicken hunting yesterday at about 8-8:15. The humidity was moderate, the sky was clear, and there was a medium-strong south wind. There were plenty of small ponds on the pasture we hunted and I do watch for algae. It probably mid 80s when we decided to head back to the truck at about 10:15. We were at one of the ponds at that point, and my friend's Griff laid down in the water for a bit. Per OnX, our route back to the truck was about 1.5 miles. Part way back there was a drainage to cross with both shade and water, we took about a 5 minute break there. I would have waited longer, but the dogs acted like they were ready to move on. It was another 200 yards to the last pond and then a solid 1/2 mile to the truck. Garmin showed about 12 miles for my dogs and about 8 for the Griff.
I was thinking about the risk on and off, and I'm comfortable with what we did. I had water for the dogs but didn't use it because of the ponds. But that was pretty much my limit. That's just the way early chicken hunting in Kansas can be: 3 hours of windshield time for 2.5 hours on the ground. You have to pick your spot carefully because you're only going to hunt one. Forecasted highs for this weekend are 69 and 77. Maybe I'll get to hunt two spots. ?