That is a subject of debate among evolutionary biologists. We simply do not know. It is also an area of active research. The only real way to find out is to look at the fossil record, but the fossil record is notoriously incomplete. According to the theory of Punctuated Equilibrium, it is likely to take less than 5000 years, which is the limit of resolution between different layers of rocks. No biologist thinks that it is possible for a new species to evolve in a single generation, excluding the fact that polyploidy can in fact result in instant speciation. That means if a diploid species gave rise to a tetrapoloid species, it can take as little as a single generation since a diploid species cannot interbreed with a tetraploid species.
It has been around 11,000 years since the end of the last ice age and the mini-ice age of the Younger Dryas. There are some desert-adapted snake species (namely Lampropeltis alterna or gray-banded kingsnake) currently living in the Chihuahuan Desert of West Texas. The Chihuahuan Desert did not exist before the end of the last ice age because it was wetter and the area was covered by woodland. That means this species only evolved since the Chihuahuan Desert formed starting about 13.000 years ago. It is doubtful that this snake took the entire 13,000 years to become what it is today. It may take as short as a few decades or a few generations for the snake to evolve into its current form .
Similarly the desert pupfish of Death Valley in California did not exist during the last ice age, since Death
valley was a glacial lake during the last ice age, instead of the hot and dry desert valley that it is today. That is another example of a new species evolving since the end of the last ice age. the old way of thinking was that a species gradually evolves into a new species, but that view is inconsistent with the need to adapt quickly to the environment. If woodland turns into desert within a few thousand years or less, for example, a species that must take much longer (e.g.100,000 years or more) to adapt to the new environment would become extinct without any descendants instead.