An opening scene states the story takes place in 928 A.D. China during the latter part of the Tang Dynasty, but the Tang Dynasty lasted from around 618 to 907 A.D.
When the Empress is dressing for the Chrysanthemum festival. Bobby pins and hair pins are visible in her hair. They were not produced until 1916. Chinese are noted with other decorative adornments to hold their hair in place such as combs and other trinkets seen in the movie.
Given Chan leaves the inn almost immediately after Wan does, why does it take so long for her to reach the palace? (Consider everything that happens to Wan after he arrives back but before Chan arrives.)