Finally seems to be the key word. We have such a finite experience on earth that we think a couple of hundred years is a long time, which is less time than the finches have been observed, but for speciation, the time spans may well take orders of magnitude more. I don’t know how many years it would take, as it probably would vary, but suspect a range of 200K and up for most to truly develop as new species. Dogs are sort a sub-species of wolf, as they still interbreed, but is thought they separated about 18-32 thousand years ago, and have had help from us in differentiating and breeding.
It is difficult to understand deep time but that is the key ingredient.
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