The last time I rode it was last Sept. and it took between 2 to 3 hours. It's a bit of a grind with 5000+ vertical but Oct. is a good time because the temps are cooler in the lower parts. Bring some warmer gear for the upper descent. Also there are some wide cracks in the road in the lower section so watch your speed coming down that area. Not much traffic that time of year.
Have a great ride and for an even bigger challenge try the Horseshoe Mdws road.
