When Does "Hero" (2002) Take Place?

"Ying xiong" (released to English-speaking audiences simply as "Hero") is a martial arts fantasy historical fiction (wuxia) film written by Yimou Zhang with Feng Li and Bin Wang and released October 24th, 2002. 

It takes place in the year: 

227 BC 

We know this because 227 BC is the year Qin Shi Huang, the first emperor of a unified group close to what we would today call China, was attacked by assassins in outlandish ways. The exact circumstances of those assassination attempts in the historical record are very different but they follow a similar pattern. 

This is the frame story, within which three tales of three assassins are told. The first is specifically said to have happened on "the fifth day of the sixth month", presumably within the same year as the frame. Nearly all other flashbacks occur after this point. 

Wikipedia places it within the wide range of 227 BC to 221 BC. An excellent episode of the "History in Film" podcast examines its exact setting.