What are target times?

A goal under every puzzle, for example "Target 12 min". It comes from the puzzle's level and type, adjusted by its measured effort compared with the other puzzles of the same level in the book (never less than three quarters or more than a third above the level's time). For example a 9 x 9 Easy aims at about 8 minutes, an Evil at about 50, a killer Easy at about 20, a samurai Hard at about 90.