Use point lights with falloff. Poser's "out of the box" lighting are distant lights, which don't make any sense for night scenes.

Turn 'em all off, and place lights yourself.

For stuff like lit windows on a building, instead of placing zillions of lights, you can do a texture map for ambient-- that'll light up the windows without the render cost of the lights.

Remember, in a city night scene, there are zillions of visible light emitters. Its very different than a day scene, where most light is coming from the sun, either directly or reflected.

Getting night scenes right is mostly about getting the lights right