I tested out XxWallaWallaxX's claims extensively on how to open the portal, and they seem to be false. However, I did discover that after fighting Atheon, if you go into the portal (past or present) that you killed oracles in during the fight, you no longer get blinded. Perhaps if you kill oracles from the past and present to cleanse the timeline, then you can enter both portals after the fight to somehow free Praedyth.