I mean, if it wasn't for the efforts fighting any nuclear plant construction at all it wouldn't take 20 years, most of that is getting approval and jumping through hoops last I checked.
That doesn't change the reality of it. When dealing with concrete proposals, you're meant to account for
all real-world influences. e.g. there's literally zero point talking about how quick it would be to build plants if
people didn't exist and you didn't have to account for them. We're talking real world, not idealized equations.
20 years is what it takes, and that's that. e.g. it could be
instant if we had a robot slave army who can shoot concrete out of their arms. But that's not reality, any more than hand-waving away the
human interaction part of it is reality. Every limit is in fact a real limit, whether that's the fact that there are limits on how much labor you can hire, the machinery you can use, or the regulation you need to go through to get the thing approved. After all, power plants are
for society, so naturally, society has a big part in the planning for that, and you can't just hand-wave away the interaction-with-society bit as not being "real" because it's not the physical pouring of concrete.
Labor supply is political, being allowed to use materials is political, the
funding to make the plant a reality is political. everything is political. You can't hand-wave it away as not being a
real part of the process of making the plant.