Excerpt

...all the chips into a plastic bowl and let set in a warm dry place for 24 hours. This 24 hour time period will give the potassium nitrate time to recrystallize and harden up before granularization takes place.

This 24 hour time period is the minimum aging time. Aging time will depend on the humidity in your area. If this aging process is not accomplished, the black powder chips, when placed in the rotary separation mill, will just return to dust instead of being broken up into grains