Knowing if first R1b-L23 were already IE speakers is another question.
More than a date could check the IE languages adoption in West. Someone say that the toponymy/hydronymy of N-E SPain in the later Iberian culture lands are of IE origin. Si I would easily buy the idea that western IE archaic dialects were spoken in Iberia and the Great isles (Britain Ireland) at since the 2500's, often in association with the strongest of the BB culture even if not from initial BB culture. It could correspond to proto-Lusitanian, proto-Ligurian, Northwest-IE, even proto-Celtic and proto-Italic, proto-Venetic and Proto-IE Rhaetic (not the etrusc-like) or a common stage of these last ones. A large sprachbund among not-IE languages of autochtones. NO way to be too affirmative because other periods, as IA, could have send these IE languages, in absence od writings, but in general hydronymy is not a bad marker of elderness. Iberian culture doensn't seem born in NE SPain, rather in E-SE I think. In NE it overtook over Aquitanians and Ligurians.