I'm so sorry, it's me again :-(
Now the number of games in each difficulty again reduces with every game, however, there is no waiting time inbetween.
I looked at the cooldown info, that said "Available now!". I was a little bit disturbed, because I couldn't believe that so much time had already passed since my last game. Of course I played. It felt off and I tried, if I could play again by clicking "continue". It indeed let me start another game right away.
RESOLVED