That gets better and better. 30-50 years with blueprints, using the HoI2 terminology.
From what I seen, NK started with military nuclear research in 96. The work was intensified after sanctions. They used theirs dual purpose nuclear plant to manufacture test materials, and well it took them few attempts to get it right.
They are actually better than US, because after few years they reprocess their spend nuclear fuel.
2 times, to be precise, given the $12B GDP of NK according to google. And since the NK population is pretty much left alone to feed on whoever they can catch, their gubmint can spend half the GDP on nuclear research alone.
Well they needed money on missiles as well, isn't it. And don't forget Fertilizer. That has been theirs major spending, and you can easily find how much they paid for (fertilizer) non nuclear stuff.
Even France and GB did not, despite up to date education and faciliies, a plenty of bright minds and first world GDPs. Because they didn't have Einstein, Fermi and Oppenheimer working for them, duh.
Sorry, you just can't turn Pepe the Village Priest into Oppenheimer in 12 years, no matter how many jewgold you pour into him.
Well this is actually a great argument for research teams in HOI. Occasionally a people without school education that had talent appear, and even piss poor country like MAO China, could have some geniuses.