Mitigated? What does that mean?
0.1 times as long sounds … buggy? 
“mitigated” means “compensated for”. You could mitigate losses of water in a pipe by pushing more water through it, for instance. You still have a leaky pipe, but the other end gets the required amount of water. Note that a mitigation might not compensate to 100%, so even though you’ve taken some measures to handle the problem, you can still have some problem left, although to a lesser degree.
A guess is that some book compensates for the missing competence.
0.1 times normal and still 13½ hours doesn’t sound reasonable, while 10 times normal might be reasonable.
assumedly you either have a book which has a recipe, and your character is following that rather than using your skill, OR you have so much skill in the particular skills that you don’t have a chance (or as much) of failure.
Maybe it’s “0.1 times less” faster! 
Maybe someone got confused about the difference between 10% longer and 10% as long.
Well, 1.1 yielding 13 ½ hours seems excessive. 1 / 0.1 = 10 times would mean standard time would be between 1 and 1½ hours, which I would consider reasonable (I’ve never made a quiver IRL, though).
The original recipe is 6h. 13.5h is 2.2 times that.
I suppose one could craft a really crude quiver by bending a pi*10 cm = 31 cm long sheet of metal into a circle, then putting it into one of the leg holes of some scrap pants and crudely sew off the bottom. Probably can’t take more than 30 mins.