These engineers must be from a different species - my experience with HW is that it's very hard to change anything in a week, especially when you're building 100000. Then again, they have everything under one roof so they can probably just walk over to the PCB designer and then walk some more to the guy setting up the manufacturing equipment, who has reels of every known component in stock. I'm curious what they chan…
If you fab the PCBs yourself and pick and place the components yourself, you could make an electronics change in one day as long as you get the design right the first time and you had ordered the components in advance.
Changing the case shape would be harder to do fast, but could still happen in just 2-3 weeks if you have your tool-making and injection molding both in-house.
The reason anything takes longer for most companies is due to outsourcing, with all of its communications delays and shipping delays.