I don't know the answer either, but in my experience they sing at first light.
I live on a lake. Some do call at night. Full Moons, Mating seasons, but most sing at first light, especially the hungry chicks.
This seems
Notable
Cemex, Epstein, Clinton connections
The fact that there is no captcha circle jerk is reason enough to migrate. FlapJack has forgotten WWG1WGA...