As one data point, one of the UK's in-development nuclear power stations, Hinkley Point C, was announced in 2010, plans approved by the owner + government in 2016, and expected to be operational by 2025 (no idea if that's an accurate expectation or not). https://en.wikipedia.org/wiki/Hinkley_Point_C_nuclear_power_...
So a bit less than 20 years, even including the 6 years between announcing a site and actually confirming plans to go ahead with it.
Another reactor of the same EPR model family that EDF is building in Flamanville, France, started construction in 2007 with commercial introduction originally scheduled for 2012 but now delayed to 2023 (no official statement with that date, but fuel loading is estimated only for the end of 2022 and it takes a few months after that). It's also five times over budget (€19.1bn, original estimate was €3.3bn, for one reactor with 1.6GW of electrical output).
Yet another one, Olkiluoto in Finland, began construction in 2005 and is also not finished, with commercial introduction planned for 2022. Its cost is estimated at €11bn, but was supposed to be €3bn originally.
The two operational ones, Taishan 1 and 2 in China, took 10 years of construction, too. It was planned to take less than 2 years.
I know little about the subject, and it would certainly make sense for it to be running late with a pandemic going on, but it seems like 5 years is a typical prediction from start of building to being in operation according to this page: https://en.wikipedia.org/wiki/Proposed_nuclear_power_station...
The planning and getting approvals actually takes longer than the construction itself.
