Russ Ouelette agrees with me on the following, so it's good enough for me. It is the general belief (with some notable dissenters) that briar pipes should be rested for the number of days as the bowls smoked through it. So in other words, smoke a bowlful in a briar, rest that pipe at least a full 24 hours; smoke two bowlfuls, rest it 48 hours, and so on.
Although I understand the spirit of the advice, it actually makes no sense. The advice taken at face value, the only sensible thing is to only smoke one bowl, and let it rest for 24 hours. If you have to let it rest that long after one bowl, why ever smoke two bowls through it consecutively? If, at work, I smoke 3 bowls through the same pipe, which I often do over the course of 8 hours, I am over smoking it.
I would consider the amount of rest needed is more related to the type of tobacco, weather or ambient temp and humidity indoors, and what sort of after smoke cleaning you are doing to it. If you are smoking straight burley, wiping out the bowl and running a cleaner through it, and the environment is relatively dry, you could likely run bowls through it constantly as long as the pipe cooled well between bowls. Especially if you gave it a nice cleaning and day of rest every week or 10 days.
Smoke a heavy aro, be haphazard on your bowl and stem cleanouts, and smoke in a wet or humid environment, and I bet your pipe gets sour pretty quickly.