The 12 hours (in truth it was 17 hours, 12 hours is only a speech, sorry) are from about 130 km behind Manaus to Humaita, not all the way from Manaus to Porto Velho! When I said "hard drive" I meant average going with over 80 km speed, as I was alone in the car I had only to look for myself. But the fun actually gone, still is a nice drive to the landscape and so on, but no more Off Road fun!
Regards