Ah! That's the magical question!
Someone was actually talking about this before, wondering if they could just "apply the lightmap" to a section so they entire lightmap doesn't have be created.
The really good news is that once you do this for a build, there is virtually no time when it loads (loads real quick). It is when you build that it takes the time.
Hence why I asked you Loads or Builds.
Do you fully understand what happens when creating a lightmap? It's really hard on a computer to make (which is why it takes so long)
-This...is my boomstick!