To add on,
In general, for a week of vacation you can Extend (add) an additional 3 days off.

For a 19 day month, that leaves you with 9 days of reserve to sit, somewhen, somewhat at the mercy of CRS. In General, I’ve had great success with CRS honoring my requests.

Sliding/keeping/waiving buffers controls the days that CRS are prohibited from placing an R day when they reconstruct your R line during the processing window.

And, in a recent grievance win, if you keep the buffers, CRS is prohibited from moving an R day into the buffer during the flying month