How common and fast is aetheryte teleporting?

[Brightamethyst]

If pressed, there's likely a LOT of holes you can punch into the story - for example, Hien's nick-of-time arrival to support the siege against Ala Mhigo castle; it's likely that he and his followers were NOT attuned to any Eorzean Aetherite (possible, I suppose, but unlikely), yet they somehow timed their weeks- or months-long journey to arrive just as the Garleans started to mobilize their air force.

Yeah. I remember questioning that at the time too. The game is usually very bad about showing the passage of time (blah, blah, time bubble, etc.) As players we see time passing in an instant even though on an intellectual level we know that it must be days or weeks or months between story events.