"Around the Time Of..."

Yesterday I sketched a dispute over the translation and interpretation of a passage in the Timaeus. Mahoney's reasons in favor of the standard view seemed strong. But Sedley has a rejoinder. Recall that the passage is Timaeus 90d1-2:

...ta_j peri\ th_n ge/nesin e0n th|~ kefalh|~ diefqarme/naj h(mw~n perio&douj e0corqou~nta...

Against taking the highlighted phrase to refer to some time, viz. "at the time of birth", Sedley objects:

...the only point of a chronological peri/ could be to stress the approximateness of the temporal reference--"around the time of ...", and I cannot see what would motivate this in the present context.

The point is strengthened when one considers that Mahoney, as was said, wishes to understand Timaeus 90d1-2 as referring back to 43c-e, and yet in that earlier passage Plato speaks of the corruption of the revolutions in the head as occurring at a definite point in time:

The motions produced by all these encounters would then be conducted through the body to the soul and strike against it... It was just then, at that very instant (kai\ dh_ kai\ to&te e0n tw|~ paro&nti), that they produced a very long and intense commotion (c4-8).

So why would Plato have referred indefinitely to something he takes special pains to identify as occurring at a precise time?

Tomorrow I'll give the reply that Mahoney develops in his article.