I think a good way to look at it is that communication is "hard wired", but language grows over time.
As for a time scale of language developing- what you might call a "language" is subjective, communication has likely existed for millions of years as we can observe it in highly diverged species (dolphins, birds, etc), but I think if we had to make a connection to guess the development of complex language we should choose the development of art- earliest art we know of is in the 40,000's years ago range, and the beginnings of alphabets are about 5,000 years ago.
If you reject art representing complex language, we're looking at a range up to about 1 million years ago, when tool use diversified. Anything before that and our only known tool was a sharpened rock, I doubt we had anything more complex than "rock smash" (and even smash can be done with a gesture, so probably just "rock").
This is how long language took to grow into what it is now with the knowledge being passed down throughout tribes and to every generation, I don't think a group of newborns today could be much more successful. Of course, they are much more equipped by evolution than people 1 million years ago, but not much more than 10,000 years ago when there was still no [known] alphabet. Also I think most evolutionary adaptations are in the learning of language, which we know children to be so proficient at, and not necessarily the creation of.
It is very difficult to find a bit of language used today that is not derived from previous language, and this is even with a simple 26 letter scheme to construct from. We are heavily geared toward learning and connecting languages, and not at all towards creating them.
thanks for really interesting topic