When did the event related to Rurichiyo Kasumioji really happen?
It's a filler arc, that does not contain canon material. The anime creators were forced to insert this new arc randomly in the middle of the Hueco Mundo arc as the anime was catching up too fast with the manga.

However, I think it's safe to say that it occurs in the tiny window between Ichigo's training and Orihime's kidnapping, as Ichigo uses his hollow abilites, and Orihime hasn't been kidnapped yet.