I would think the 120 hour figure is closer.Not counting install, I was thinking around 100 hours to build & finish.
Who are you?There could easily be 120 hours of shop time.
I would add another 16 hrs for your drawings and layout.
Delivery is another unknown. How large of units can you get in the room? Is there direct access or is all this coming down those stairs?
If you are building on site, I think the labor time is light.