Comment by jpgvm

It's also an average over a bunch of different reactor technology, not all of which takes the same time to build.

The main designs they are employing are from the Hualong One, soon to be Hualong Two line. Hualong One takes around 5 years, Hualong Two is a revised design intended to reduce costs and construction time to only 4 years. Which is still a long time in absolute sense but is practically instant in nuclear reactor timescales.