Point taken, my experience in the kegging realm is limited (my first three kegs were done like this due to an extremely impatient new kegger) but my line of work deals heavily in dissolving gaseous components (from compressed calibration gases or pump-drawn process gas) through all kinds of liquids.
My point was that there are some ideas about burst carbing like this out there that don't have any basis in science for offering advantages over other methods, such as connecting the gas to the dip tube, or running the pressure up so high if you are going to shake the keg. If you are going to let it sit, then sure high pressure will help speed things along. But if you are shaking it anyways, equilibrium will be reached pretty quickly no matter the regulator setting. So, I was simply supporting the method already offered to set the reg at your equilibrium pressure (according to the chart) and shaking until you no longer hear gas being supplied by the CO2 cylinder.
Sorry if my phrasing was unclear, I am not recommending setting pressure to a level higher than would achieve your desired CO2 volumes according to the chart, ever. You are right, the details do matter. But since my first kegged beer was 3.8 gallons of Mild in a 5-gal keg carbonated to 1.8 volumes, and my second was a full 5 gal of saison carbonated to 3.5 volumes, I am pretty sure that 100 seconds would have been wrong for both of those. There are way too many variables to be able to assign a hard rule to this process. As you say yourself..
...attempt to quantify...
...unless you want to add mass flow controllers, NIST-traceable thermometers, and much more sensitive regulators and gauges than homebrewers typically use, you will not be able to "quantify" much about this bursting process. Trial and error has led you to your 100-second method, and as I've said I can't claim to have the same experience to draw on. I was just offering an idea that makes logical sense and is impossible to over-carb and pretty easy to know when you are at or near the desired carb level.
But who know, maybe once I do have a few dozen more successfully kegged batches under my belt, I could come back with my own 105-second rule..