It took me about 3 hours to do the upward stairs for my design.
Considering I use the second attempt, I would say 6 hours total.
But the way I did the downward stairs was very simple because the perspective didn't let you see any of the stairs themselves, just a 'hole' into the level below.
It does get quicker - at a point you will get a feel for the perspective walls. Really. It will happen.
