Ok, I got it, I have to start playback and draw a tempo map in real time in the tempo view. Awkward!
But now I got problem on Audio:
I made sure "Import All Audio As Groove Clips" was checked. Then I dragged and dropped a freshly recorded audio clip into a cell. When played through by the cell it is slower than if played in the track view. And with some artifacts (some kind of chorus-like effect). Why is that??