There is no time where a system run on hydraulics or electric motors are ever “locked in” on a rate.
Most are driven by PWM valves that are opening and closing 120 times per second.
So based on speed, desired rate, density of product, etc, a desired rpm is calculated probably something like 10 times per second.
Then it will adjust how long to hold the valve open each of the 120 cycles per second to maintain, then check resulting rpm and recalculate a new target rpm.
With slightly changing speed and chasing the proper rpm, a slightly changing target rate is the least of the worries for the system.

Michael, the default of 100 rates for the GRX should be fine for most any items going through an air seeder. I very seldom change this value. 
Agree with Darin. I do almost all my maps as “interpolated” up front. I will add in hard breaks after they are built for 2 reasons. 

1. Controllers with limited polygon count / rate issues. (using “Round to Increment” getting # of rates to 10 to 15 rates)
2. User Preference – Mostly “Row Crop Planter” (not seeder) doing 500, 1,000 or 2,000 seed breaks on corn seed or 4,000 or 5,000 seed breaks for soybean seed. Bit of an old school concept to look over the row monitors to see how they are applying. 

Other than these two reasons / issues I send everything out interpolated. Also, at the end of the field you will find out that the interpolated maps usually are closer on the “total lbs” applied to the “map lbs”. I like to use the shooting adage, “Aim small, miss small”. With the hard breaks you get on one side or the other of a large break and it can make for the controller being in a 100 lb zone or a 200 lb zone. So 55% of the units in the 200 lb area the whole drill is doing 200 lbs, and you have that happen a few times where you are on the “High” rate side and you are short on product. One more reason to use interpolated. Getting of point a little here, but confirming the idea of interpolated!