Let the number of days planned initially to complete the 360 articles be \( N \).
Therefore, the number of articles to be made per day originally is \( \frac{360}{N} \).
With the new plan, they make 4 more articles per day, so the new number of articles made per day is \( \frac{360}{N} + 4 \).
According to the given condition, with the new plan, they will complete the job one day earlier, so the time taken in the new plan is \( N - 1 \).
Thus, we can set up the following equation:
\[
\frac{360}{N} \times N = \frac{360}{N + 4} \times (N - 1)
\]
Simplifying the equation, we get:
\[
\frac{360}{N} = \frac{360}{N + 4} \quad \text{so,} \quad N = 36.
\]
Therefore, they will complete the job in 9 days (i.e., \( N - 1 \)).