Ye, these builds are right.
And about the timing, i don't really know.
I boosted my friend from lvl 30 because we wanted to play together. But that took maybe 2.5 hours with events and a little bit of looting and dieing. (he only had a xp socket i think)
In nightmare, its as easy as just walking through depths 2 since strafe is auto-aim and FoK can be used on the move.
in hell, you might need to stop for a multi shot for big groups.
And also, for the natalya's 4 set piece bonus, i didn't find it necessary (I don't even think i had it), since you get a lot of health globes which means a lot of discipline from vengeance, and with the 50-60 build discipline is really no issue.
Ok, the result is in. Did a 4-man group boost and this char with max gear dinged 60 in 2:00 hours. 1.08, no anniversary buff.
This was done with tempest rush monk from 1-50 and archon wizard from there.
Just saying, it is no world record attempt, but it was done with the help of this guide with teh goal of being effective
Just to add a little bit here. This could easily have been done in 1 hour 30min without spending to much time fixing gear and ressing nubs that likes to run into molten and such. 2 hours is still good but with some focus this could have been done faster.