Maybe this part of the wiki is what you are looking for : https://wiki.factorio.com/Enemies#Evolution
I think if you increase the evolution => pollution settings, you are telling the game to make the biters react faster to the pollution, evolving and attacking more often. Pollution being one of the factor that increases "evolution". I think your words refer to that setting which makes pollution increase "evolution" faster.
It doesn't change the pollution produced per machine the same way modules would do i think.
For when the pollution of a machine is changing , even though it may say how much pollution a machine produces per minute, i think the game counts the pollution for every tick, which is 1/60 of a second. This in case you have a machine that turns on and off very fast. If during a minute the machine is running half of the time only, it will produce around half of the pollution. If during a second the machine is running only half of that second, same thing. I'm not sure though because it says the pollution cloud is updated every 64 ticks there https://wiki.factorio.com/Pollution
. I believe the update of the cloud is the sum of the pollution produced during the last 64 ticks where each tick the machine produces more or less pollution if it's running or not.
For the sake of precision, the "drain" is always active consuming energy, and i think producing pollution. Most the pollution though comes from when the machine is running. I guess the pollution per minute figure is the max amount when the machine is always producing (aka "at full power"). If the machine is connected to electricity but not producing at all i think the pollution can be calculated with :
[drain/max consumption]*[pollution per tick]*[number of tick]. where for a minute you have 60 second and also 60 tick per second.
Or [pollution per minute * number of minute] or [pollution per second * number of second] which as you noted require conversion of units.
The game counts time in ticks, the electricity uses Joules and Watts, which require using second, and it's easier for pollution to think in minutes or hours. There is no way around unit conversion for precision, but maybe you don't need to be super precise to gauge pollution,i guess that's why on the wiki they just say the pollution per minute for machines