There are a million factors on how well a heat signature shows. The temperature of a spot (animal) is measured against it's surroundings, the temperatures are displayed as color changes on the screen. At a time the surroundings happen to be the same temperature of the animal, the animal would not stand out. When there is a large temperature gradient. between the animal and it's surroundings it would stand out. So, many factors come into play including air temperature, shade vs, no shade, type of surface in the background, etc. I fly a drone for law enforcement, thermal is a great tool, but like most things, it works best for trying to find a moving object, it catches the eye. Also, thermal only reads the surface of things, it does not penetrate. For example, you can't use it through glass to see what's inside. So, a tree canopy will obscure things below.
It sounds like a great idea, but I think you would be disappointed. Also, many of the lower end thermals are useless for about anything. (Mavic 2 Dual). You have to have enough resolution. That said, I can see a rabbit in a soybean field from 200' on the right nights. In my opinion, daytime usefulness is very limited.