Probably after the Anschluss. Although Hitler had already violated the Treaty of Versaille by rebuilding Germany's military and moving troops into the Rhineland, the annexation of Austria was the first big territory takeovers and as a result of the Allies inability to punish Hitler for this violation of the Treaty of Versaille, it allowed him the momentum to quickly overtake Lithuania, Bohemia, Moravia, and Czechoslovakia. Which of course leads up to the invasion of Poland.
