The length of time that you should percolate coffee on a camp stove or fire depends entirely on how strong you like your coffee. When the percolator that you’re using to make your coffee begins to boil, the steam that’ll start rising from the spout and the bubbling noises that it’ll start making will make you acutely aware of when the water inside it has reached boiling point, either turn the heat on your stove down or move the percolator to the edge of the fire where it’s slightly cooler.
Ideally, you should then leave the percolator alone for ten minutes to finish brewing your coffee and when that time is up, remove it, carefully, from the stove or fire and pour your coffee. That ten-minute window is enough to ensure that you’ll get a cup of perfectly percolated coffee. However, if you prefer your coffee a little stronger and more akin to rocket fuel than the average cup of joe, give it another five or even ten minutes on the stove or the edge of the fire. And remember, the longer you leave it, the stronger your coffee will be.