I did that ride earlier this year - deciding to do it in one day!! First snag was a road closure for construction about an hour out of Cajamarca, which I was told would last around two and a half hours! Some nice highway police told me there was a detour I could take to get round - and this led me across fields, along a boulder strewn road, through soft sand and mud, and to a spot where two men were digging a wide trench across the road (they kindly bridged it for me with a couple of small tree trunks!), but it did save me over 90 minutes waiting time when I rejoined the road! May now be tarred all the way, but when I rejoined there was a couple of miles of (very good) dirt road, where the guide books said it was all tarmac!
Potholes are a major problem in the Maranon valley, where landlsips have brought boulders down across the road, but generally I found the traffic extremely light so the narrow roads and hairpins were not an issue.
Expect to go from cold to hot, wet to dry, during the day!! Very hot as you descend the Maranon valley - twice the depth of the Grand Canyon!! Also good idea to ask directions in towns as roadsigns are few and far between (non-existent!). Amazing scenery!!
Took me 9 and a half hours all told on a Ronco Demolition 250, bought in Peru, and was I glad to reach my hostel in Chachapoyas!