Recent relevant discussion: https://news.ycombinator.com/item?id=34015330
Tl;dr: this is not true; nuclear can be build quickly enough. Also, "The best time to plant a tree was 20 years ago", "But the second best time is now".
All these discussions centre around changing policy but I have heard very little about actual change happening. Further, we have very little expertise left regarding building nuclear plants so even if we could start building as many reactors as we want, how would we? Then there are the financials, which are heavily compounded by the policy and lack of experience.
Since we need the policy to change to build more, we need to build more so we can actually predict the costs/time, and we need to predict the costs/time for the financials to work... And nothing seems to be being done any of it.
How exactly can nuclear be built in the current status quo?
I live 20 km from a new nuclear power station being build. If my country can do these projects, why not others? You are right, we need political will but the political will comes from people wanted them to be built.