simulate morning & night

I have a big scenery shot with lots of buildings, grass, mountains, bridges and stuff (with a lot of display lists). I am moving around in the scene from a height, I want to simulate time of the day(maybe discrete morning,noon,evening,night).

I read about lighting, it seemed that I have to define normals to all the surfaces and then define sources of light. But I have lots of surfaces (thousands), so is there any way to simulate the morning, evenings without having to define normals to all these surfaces.

Any Ideas???

yep :
calculate several lightmaps, and smootlyblend from one to another

btw normal calculation is easy…