When is the darkest time of day?
It depends where you are. In the East, such as Riften, it can be dark until 10:00 am, but in the far west places like Rorikstead and Helgen, dawn comes at around 4:00 am, and in the middle, like Whitrun and Dawnstar, morning comes around 8:00 am. If you want to sneak around anywhere, though, 8:00 pm-8:00 am are usually fine.