I believe he heard that from a discussion on the origenal physical regulation of the rifle by the regulator at the makers factory! It matters when you are physically adjusting the barrel's convergance, while building the rifle, but not critical for hunting purposes!

The fact is when the regulator is adjusting the barrel convergance, he will start with the barrels at room temprature, and fire the right barrel first (on right hand rifle), and follow up within 10 seconds with the second shot from the other barrel. This is the only way to get the barrels adjusted as closely as he can to perfect. He will then let the rifle cool, and fire four shots in a very short time as they would be under close quarters hunting , or STOPPING conditions in the field. The rifle is then carded, and finished along with the final fileing of the sights.

That exercize is to assure he has done all he can to make the rifle work as well as is possible.

In the field your sceenario above, is asking a ligitimate question, that is amoung a group of phrases that make double rifles so confusing to many who don't really understand them. That sceen would play out as well as you can shoot, even after 30 seconds od five minutes! You are not shooting a target rifle in this sittuation, but a stopping rifle, and the proper drill is exactly as your sceenario indicates. You fire the right barrel, and your target takes a step, behind cover. You reload the fired barrel, and either wait,or he comes shortly, and you fire the other barrel, then re-load. If he has stepped out of sight, but you think he is still there close by, and on his feet, or you reload, and move very slowly till you can see him, then wait. Which ever you do, you be ready to fire that right barrel again, and the left one in rappid succession, and in that case you will likely not even see your sights, at all, but shoot instinctivly, and just off the muzzles of your rifle. The proper responce,will be what ever you do, Don't worry about how many seconds have passed, because it will not matter, if you don't do it right!