Can we tell when was PII spoken ? I read somewhere that it has to be before indo iranian split and the The two things which really anchor it are the common words for chariots and camels. Proto-chariot esque wagons were developed since around 2200 bc ish
Some sentences of Vedic have the nearly exact equivalents in Avestan. Both languages can be dated to the late second millenium BC.
This suggests that about 4,000-3,500 years ago, Indian and Iranian were more or less dialects of the same language. So Proto-Indo-Iranian was probably spoken during the 3rd millenium BC.