When exactly are you “promoviert” in Germany?
The Promotionsordnung of my alma mater says this:


  §17(1): "Als Promotionsdatum gilt der Tag der bestandenen mündlichen
  Prüfung."


(The date of Promotion is the day of the successful oral exam.)


  §25(1): "Als vorläufigen Nachweis der Verleihung des Doktorgrades
  erhält der Bewerber vom Prüfungsamt der TUM eine Urkunde nach Anlage
  2, sofern die erforderlichen Exemplare nach § 20 fristgerecht
  eingereicht worden sind."


(You receive a preliminary certificate when you have submitted the required copies of your dissertation.)


  §25(2): "Vor Aushändigung der Urkunde nach Abs. 1 ist der Bewerber
  nicht befugt, den Doktorgrad zu führen."


(You are not allowed to call yourself a Doktor before you have received this preliminary certficate.)


  §25(3): "Der Bewerber erhält ferner eine Urkunde in deutscher und
  englischer Sprache nach Anlage 3 a oder 3 b, die mit dem Siegel der
  TUM versehen ist und das Promotionsdatum gemäß § 17 Abs. 1 trägt. ..."


(The date of Promotion is written on the final certificate.)

So, you could say you are promoviert when you have passed the oral exam. But since I'm not a lawyer I'm not qualified to give legal advice. Personally, I would avoid anything that could be seen as you saying you are a doctor before you are allowed to do so. Until then I would say "I've defended my dissertation successfully and am waiting to receive the certificate." When you have your certificate, the date of Promotion is the day of the oral exam.

In practice, you get the preliminary certificate rather quickly. I believe it was something like two weeks after the exam for me, but it depends on how quickly the head of examination and the administration works. The biggest problem was getting a Führungszeugnis in time since I hadn't considered that prior to the exam.