User blog comment:B1littlehero/Speculation of the Origin of Species/@comment-7622429-20140611002324/@comment-160529-20140611064300

I dont believe that the Vex actually time travel, I think that their citidel is located in a sort of... time pocket, and that they use portals to exit it at strategic times.

This is difficult to explain, but did you see the episode of Stargate involving the replicators? originally the asgard developed a machine to freeze them in time to keep them from developing, then they inverted it and cause time to increase in the isolated pocket, allowing themselves to develop at a vastly accelrated rate.