500 hours ETA light baking time, how to significantly reduce it?

Hello sir. ma'am. I'm a newbie. In this topic, I'm talking about the terrain forge from 2,000m unity terrain with hand sculptured and unity built-in terrain texture, only 1 directional light in this scene. After hit "Generate" button the ETA number show I need more than 85 hours to complete, but the problem is "it increases every time I notice it" now the number change to 500 hours. I don't know what happens. Should I drop some setting number down to significantly decrease the baking time sir?

More intel, my sun is not moving so I know I need to cut some extravagant setting off but the problem is I don't know what that is. Please help, sir. ma'am.

 

Dramatically decrease resolution.