When to do the "Ancient Revelations" quest.

[Krauser686]

This is the quest that "unlocks" after you return the 4 artifacts to Pythagoras.
I have already done it whitout completing the "main storyline" of the family and the cult, and during the conversation between our protagonist and Layla I could see some "gaps" between dialogues, probably implying that he/she would talk about events of the main game that i could have not seen yet.
Is this quest supposed to be completed after finishing the Family/Cult storylines?
I know that the next quest related to Atlantis ("Heir of something...") is supposed to be done after the main game.