When does a species undergoing natural selection, change more?

You're absolutely right. If that's true... then genetic code would vary less.But, of course, your "if" statement is false simply because what you think happens with evolution does not happen. As explained by the other posts here. Therefore, genetic code may or may not 'vary less' and your logical idea doesn't mean anything to reality.There could be an animal (or human) that is born with a "perfect genetic code."
And then they die before they have any kids.Or maybe they have kids, and those kids have kids... but they all die in a fire.No more perfect genetic code.That's how evolution works.It doesn't matter if your genes are "strong" or "weak."
All that matters is if you survive and have kids and your kids survive.Surviving doesn't take 'perfect genes.' It doesn't even require "good genes."
Surviving can sometimes simply be lucky.
Other times it can be focused by the environment.Whatever it is, though, survival is all that matters.

Your first post tends to lead more into issues with strengths, weaknesses and the ability of evolution to continue to function in the long term.If you read the many posts responding to those problems, I hope you'll see that the questions you asked regarding them don't make much sense.In all of that, however, I never actually attempted an answer for the question you posed in the title of your thread. The basic answer is "as soon as enough generations have gone by."There really is no set time. And, actually, "never" is a completely possible answer as well.
It all depends on the selective pressures in question and the ability of mutations-occurring-during-reproduction and inheritance-of-traits to keep up.For some creatures, like bacteria, this can be in the order of weeks or months.
For other creatures, like wolves, this can be in the order of hundreds to thousands or even millions of years.It's not like a few wolves after thousands of years "change a lot."
It's more like the entire population of wolves continually changes little-by-little over the course of each generation or two. Then, eventually, if you compare the 'original wolves' to the 'thousands of years later wolves' there will be "more" change that you can see directly.But no single generation of wolves ever changes "more." That's not how evolution works.

Yeah. I kinda stopped posting-in-order-to-get-a-reasonable-response-from-specific-people a long time ago.
I generally post because I'm bored and want to express an opinion.And posting on this site makes me feel smrt.I'm one of you smart people, right guys? Guys??