Obviously those tasks are cherry-picked, but it sounds plausible. If you're building something for the first or only time (as opposed to a production line when workers have a chance to become more efficient on each subsequent build) then how much time is spent referring to the specs as opposed to actually welding a spanner? Quite a bit.
Even when helping my nephew build a brand new Lego model, most of the build time is spent looking at the instructions, finding the correct part from amongst others, and then verifying said part against the instructions to make sure it's a ten-knobbler and not an eight-knobbler. These tasks are amenable to being aided by an AR system.