NK is actually thought more realistically to be 10 years away from actually developing missiles which will hit the US mainland so there is no imminent danger.
I would be very wary of estimates like that ... in the 1940s and 50s, the USSR was "decades away" from developing nuclear weapons (first test in 1949), then China was "decades away" (first test 1961).
The UK should knew very well how inaccurate estimates can be. When the US cut the UK out of nuclear weapons research in 1946, the UK was assumed to be (wait for it) "decades away" from developing it's own nuclear weapons. As it happened, the UK (not for the first time) confounded US expectations and had an independent thermonuclear (H-bomb) before 1960.
Meanwhile, the free nuclear fusion power we were promised in the 1970s was (wait for it, again !) "decades away" still eludes us. As do jet packs and hover cars.
You would have thought that the US - who incredibly managed to put a man on the moon in less than a decade - of all countries would understand the vagaries of fortune-telling.