You'd probably have to run nephalem rifts exclusively because questing would be pointless, you'd have to sit there the whole time and babysit it along the way. Rifts on the other hand can run solo, but that being said you'll still need to pop in from time to time to upgrade your gear manually. DB's autoequip leaves a lot to be desired. Probably going to want to do it on Expert mode unless you already have decent paragon levels and access to good starting gear/gold/gems. My rough guesstimate would be anywhere between 4-10 hours. But that is only an estimate (more or less)