During the course of its development, when is a video game's box art designed and when is it rated by the ESRB?

As I beta test PC games for a company in the U.K. They usually design the cover art as they're developing the game. I see very few in boxes anymore and mostly on PC games the cover art is usually something from the game itself or they have a special designer to do this. Most get rated during beta testing as they are developed.