Hans-Karl:
I think Petre is talking about Bernadotte's complaint that the road from Dornburg to Apolda was tough going and that is the road that Hohenlohe's brigade traveled on the 13th... Not the road from Naumburg to Dornburg.
If it was 16 Km from Naumburg to Apolda, then ten miles. If he only traveled 6 in eight hours, that means at the least, the head of his march column was four miles down the road to Dornburg, and at least half way to Dornburg at 4 am when he halted the march to talk to Davout.
Bill