How do people in D&D know when it's daytime? The penalty to see the sun is well into the billions at least.
Well, even if they couldn't see the sun, they'd still be able to see the effects of the sun's
light. So it would just become light or dark periodically in their crazy world.
Of course, what would they see when they looked to the
sky? Even during day time, would it look blue? You wouldn't be able to see far enough to actually get any color from it. So the sky would always look black, but during daytime, everything within range would be light.
I'm glad these Spot rules were well thought out. We wouldn't want any
inconsistencies in our games.