Dating PIE

From Dixon, R.M.W., 1997, The rise and fall of languages, Cambridge,
Cambridge University Press, pp. 47-49:

"What has always filled me with wonder is the assurance with which
many historical linguists assign a date to their reconstructed proto-
language...We are told that proto-Indo-European was spoken about
6,000 years ago. What is known with a fair degree of certainty is the
time between proto-Indo-Aryan and the modern Indo-Aryan languages --
something in the order of 1,000 years. But how can anyone tell that
the development from proto-Indo-European to proto-Indo-Aryan took
another 3,000 years?...Languages are known to change at different
rates. There is no way of knowing how long it took to go from the
presumed homogeneity of proto-Indo-European to the linguistic
diversity of proto-Indo-Iranian, proto-Celtic, proto-Germanic, etc.
The changes could have been spoken rapid to slow. We simply don't
know...Why couldn't proto-Indo-European have been spoken about 10,500
year ago?...The received opinion of a date of around 6000 BP for
proto-Indo-European...is an ingrained one. I have found this a
difficult matter to get specialists to even discuss. Yet it does seem
to be a house of cards."

Would members like to discuss this and to guess on the time between
PIE and R.gveda or Sanskrit?