Can Echidna's ability be used during the turn in which it is purchased?
Tile effect occurs AFTER Tribe effect.
So it's too late in this case: when you score your builders you don't have the Djinn yet.

From the rules (Section 2.5 Tile Action):


  Once your Meeples’ Tribe actions are over, perform the Action for the Tile your last Meeple ended on ...