Lighting/Mapping for these requirements?

Hi.

Looking for some advice on handling lighting for a top down, 3D, PC game I'm working on, using Unity 5.1.1.

A little context:

There will likely be around 40 maps (Map A), in different urban environments. These maps are not individually very big, and represent the area the player can move around in.

In addition, there will be a smaller number of larger maps (Map B). Each one of these fits around several Map A. The player can't move into Map B, so the Map Bs are just there to create a sense of a larger environment.Map B can also be destroyed/not instantiated to cater to lower end systems.

Additionally, I'd like to have 3 light settings for each map A: daytime sunny, daytime overcast, and nighttime. 3 separate lightmaps may not be necessary for each Map B, as there is a semi-opaque boundary between it and the camera, so it will only be partially visible.

The question:

Is this feasible with lightmapping, and if so, how would you go about it? Thinking so far is to prefab each map A & map B, and store the 3 different lightmap settings, then instantiate the map prefabs when the level is created, and set the lightmaps. Does this seem sensible, and if so, any suggestions on how to got about it?

Thanks for reading!