The speed of the reflection in the steel is the starting point.
Identifying the steel in your barrel is the first step.

Regular barrel steel reflects at 18, 916 fps.
3% carbon steel reflects at 19,107 fps. Savage barrels fit this category.
4140 and 4150 stainless steel reflects at 19,979 fps.
416R steel reflects at 20,014 fps.
The Materials Handbook lists 'Stainless Steel' with a generic speed of 20,000 (probably to cover everything from 4140 and 4150 and 416R stainless).

Then you have to know the length of your barrel from bolt face to the muzzle (consider the recess of the crown as not being part of the barrel steel.)
With the length of the barrel and the reflection time of the steel, you can calculate the time to go from the chamber to the muzzle.
Then you double it to get back from the muzzle to the chamber.
Do that about 10, 12 or 14 times and you get the exit time goals for your rifle.
You want the exit time to be on an even reflection because that is when the shock wave is back at the chamber when the bullet is leaving the muzzle.

The theory is that the less shock at the muzzle give you less vibration as the bullet leaves and also keeps the crown the tightest as the bullet is leaving.

QuickLOAD actually calculates the exit time and accounts for the acceleration of the bullet based upon the powder charge as well as considering the, barrel length, seating depth and trim length on the pressure when the bullet fires.

The choice of reflection time to match against exit time is up to you to figure out.

Even though QuickLOAD is a simulation, and many questions its validity based upon that, my seven rifles, accurate enough to use exit time for loading, produce results within 0.001% to 0.002% of the QuickLOAD calculated exit time. That variation can easily be caused by the mix of carbon in a particular barrel steel or poor barrel measurements on my part.

I built a spreadsheet to calculate reflection time based on the steel of my various barrels and their measured lengths.
You have to include the length of muzzle brakes, flash hiders and suppressors in the reflection time if they are attached to the barrel.
The problem with those appendages is identifying the metal they are made of and getting an accurate measurement of their mounted length and contribution to reflection time.