In a non-nuclear confrontation how long would it take us to kick North Korea's a$$?

To answer this question ---- I go to: 'Thunderstruck, military montage'.  Your question will be answered.

Only Korea?
Do you really want to find out?

We already tried that.  It ended in a stalemate.  Just look at how well we did in Vietnam.

We tried that once and found out it's not as easy as was first assumed.

We are still at war with North Korea.
To the point CallMeIshmael and Jewels Vern made ... we beat North Korea so badly, the Chinese military poured across the border for fear we would invade China while we were at it.

North Korea is not a problem.
The problem is how China and Russia would react, as they both share a border with North Korea.