We finished the entire course, including calibration rides and driving to an from the course, in 7.5 hours. It would have taken me that long for one ride, then I would have had to go back for my second ride. I will use a co-rider for every Marathon course, and most Half-Marathon courses. (This was a loop course, so we were basically back at the Start when we finished.)
Good luck with the measurement. It is a big help to have the mapping tools available now, so you can work through most of the issues before going to the course.
Oh, I noticed "an interesting conversation...". Isn't the prescribed proceedure to have each rider ride separately, so each can take their own "shortest possible route"?
