A lot depends on our finding and targeting noko’s artillery & ada before our shock and awe first strike. Then there is counter fire capabilities. Firing an artillery round locates the source of that round before it even lands on its target. It is then targeted.
Noko’s artillery would be lucky to survive even a 2nd round of firing their tubes.
The real issue is their NBC weapons.
Let's assume a fire rate of 3 rounds per minute. How long would it take the U.S. and South Korea to take out 12,000 artillery guns? According to you, less than 40 seconds.