Well, I am not a scientist, a doctor or even particularly bright but here is what I can tell you from personal experience.
I own a dog that has bad skin. She itches incessantly in the winter, though much improved after our move. I am in Canada so long winters. And the province we previously resided in is notorious for crazy, unpredictable weather. Think 37 above to 17 below with 15 inches of snow within a few days. Just some background for you.
In any weather that permitted I made a point of getting her outside just to soak up the sun for at least an hour. Coat would improve, bald spots from scratching healed and grew in within days, she slept better, her eyes brightened up and her appetite improved. This is aside from her regular exercise and outside time, this was time I freed up during the sunniest part of the day to simply let her lounge in the sun, in all 12 months of the year.
To state that wild canids are nocturnal is misleading. Wolves and coyotes are frequently out and about during the day, hunting or just touring about, and have been seen sunning themselves. Dingoes are also active during the day, as are African wild dogs.
Hunting takes place when prey are about, it has little to do with time of day.