If you did Gnomeregan, you'll be offered the introduction quest by the same NPC (the ones with Mana-Poof on their side in Boralus or Dazar'alor). Then you go to Eastern Plaguelands and to the side entrance of the Straholme dungeon.
And I hope we are clear that you'll not find this on live servers right now, this is 8.2 content so you'll have to wait for 8.2 release or test in on PTR.
It's shorter than Gnomer, I'm thinking. I've never done a timed run in Gnomer, but for Strat I ran it at around 20 minutes using teams pre-loaded in Rematch, their corresponding scripts, and wasting no time starting the next fight.