The stubborn muscle seems to give up in time. It's not yet perfect but today I was able to jog for 15km without any serious problem. Still I hesitate to make the booking for next weekend. I think I will wait until Wednesday.
However, I finished more than 400 races so far but I have never been prepared so poorly before a really challenging event. My only hope is that routine will help. At least the time limit will not scare me. The Karwendelmarsch is also open to walkers what means there are provided 14 hours to complete 52km.