Speaking for Germany: in former times, a "Habilitation" war required for a fukk professorship - which you usually wrote during your post-doc phase. It usually took about 6 years (of course with strong variations). Now, you can qualify for a full professorship by beeing a "Junior Professor" - which takes 6 years with in interims evaluation after three years. In some cases, junior-professurships can be transformed to full professorships after six years, but if this really happends depends strongly on your univrsity and faculty (in fact politcs says it should be the norm, but in fact universities are having much more junior professorships than full professorships).
So the general norm in Germany is 6years+, since you usually won't get a position right after your PhD.