Terrapower just broke ground on a new reactor in the US, it's expected to be completed in approx 6 years. Even with significant delays it would be under 8 years and almost certainly under a decade.

While not touching on cost, this link shows how much more power generation you can get with nuclear compared to other sources of low carbon energy over a decade of deployment. If you need to generate a lot of energy relatively quickly and don't have amazing hydro options, nuclear appears the most scalable.

https://scienceforsustainability.org/wiki/How_quickly_can_we_build_clean_energy%3F