We have here a time line beginning in between 2900 BC and 2500 BC, you figure these dates are all estimates so there could be a few hundred years in variation concerning the current dating.

R1b1b2a1b* estimated to be 2490 BC, I'm not sure on the margin of error for this estimate, but if you figure it as an estimate it could be 450 to 10 years off for its earliest appearance. Either way it's not too far off in terms of dates to be a Bell Beaker candidate.

The Bell Beaker Culture is often suggested as a candidate for an early Indo-European culture, more specifically, an ancestral proto-Celtic culture.

Basically we have Neolithic carriers of R1b1b2a. This haplogroup later mutates into R1b1b2a1* during the later parts of the Neolithic and stagnates/doesn't mutate further around the time the Bell Beakers first show up in Portugal, Southern France, and Northern Italy.

By the time the Bell Beaker culture spreads into areas of Britain, Spain, and Central Europe we have R1b1b2a1b* carriers descending from the previous R1b1b2a1* Neolithic-early Bell Beaker folks, these people of the Bell Beaker Culture being proposed ancestors of the Celtic peoples.

links of interest:

http://www.familytreedna.com/public/...ection=results (this one is the r1b1b2asterisk project, it has a bunch of dates and migrations listed on the results page, it contains both more current and older theories)

http://www.familytreedna.com/public/...ection=results (this is the R1b1b2a1b and subclades page, very good for distribution maps of modern R1b1b2a1b's and subclades to see where all the descendants wound up at)