Well, right now I'd just wait if I were you, because if you did successfully preorder it, you'll get an email saying you can play it, and it'll appear in your "My Games" in impulse. If neither of those happen within the next fivish hours, chances are you did not successfully preorder it.

It never hurts to have more information, but I wouldn't write the email until the morning (or... in 7-8 hours, whatever that is for you). If you still haven't gotten your key by then, it's worth checking into.