The first UV set is used for your textures by default and the second set is used for lightmaps by default. That can change, but they are typically called UV channel 0 and UV channel 1.
What example project are you trying to bake lighting in? I’ve gotten anywhere from 45 seconds for a small scene production quality, to 30 minutes on some of the content examples.
Example project - this project in my last picture…I just droped some material in floor, but this project comes with Unreal engine.
Forget about this, maybe some glitch.
I will try when I get time to solve this, yesterday I see that only problem is with my uv channel, because in engine my channel looks prety bad, sory for my boring questions 
What is:
By defalut, it is set to “0” and “1”.
My model is on uv chanell 2, created in 3ds max.
UE4 just reads the UV channels in the same order they are in your application starting at 0, it doesn’t matter what they are named, if you have extra channels, delete them. If you just have one UV channel it’ll use that one to generate the light map UVs, which should be fine for a fence.
I will try few things, I’m prety sure that somewhere I miss something in export/import.
Is there something execpt uv chanell - what is need to increase/decrase when I import something to UE4?
I founded my error.
First, because I have my second uv chanell created in 3ds max - I must uncheck option “Generate lightmap UVs” when importing into engine, and then in mesh editor set UV chanel to “1”, because this is my second chanel in 3ds.
Still have to properly unwrap mesh in 3ds, because I have overlaping uv’s.
(i’m idiot, I was unwraped my model in 2 steps, first my vertical planks, and then other beams of my model…of course, now I have overlaping uv’s, obiously I must unwrap my model all at once)
Oh so every step I must have some error or ******** in my project.
Ok, I learned a things about good unwrapping, a good lightmapts etc.
Now when I import my models, dont have lightmap issues, overlapping UV’s etc.
But now I have bad shadows in my landscape.
In my imported models, and models what comes with unreal engine (yellow chair, lamp etc).
Only when I create static mesh from BSP inside engine - works good.!
Something like this:
I increased the lightmap resolution to landscape to 4, yesterday I was trying few thing to increase in my models parameter, but nothing helps.
Same thing with unreal stock models.
But when I import all that models in my second project, in that landscape everything is good. When I compare options of this two landscapes - everything is same!
And same blueprints codes are same, everythin!
I there something what can do bug in landscape shadows or just try to deleate my landscape and create new?
Uhh I forget!! Maybe I change some option in my directional light awchhhh…I will look that today!
So at least my shadows are working great, without any strange shadows etc.
But what is your opinion, which way is better for optimizing game when I have model with various materials to avoid UV overllaping?
export model with multi sub object
just use “render to texture”, use diffuse rendering, and import model in engine without materials, just with UV channel, and then import that diffuse baked texture and create material inside engine and put it on model?
I used second options, I have four materials, just bake diffuse texture, and import model without material.