I'd need more context however what i'm immediately struck by is the word atomistic. Just doing some cursory reading of Whitehead I think it follows that he would generally say self determination of the human being is all down to the inherent perceptions of that human beings reality that may be taken from causal relatedness and casual efficacy of nature. Human beings, according to Whitehead, inherently use and need symbolism or symbolic reference to discern meaning from anything.
"but the physics of the universe are infinitely and densely divisible"
I believe what this is referring to is the concept that any discerned symbolic meaning by man towards self determination is as infinite as the laws that make up the things that man perceives. I see stars in the sky (nature) and determine self from them in depictions of gods and goddesses of them but at the same time I develop a satellite to view a black hole in space. if the physics of the universe is infinitely divisible then I can infinitely take meaning from infinitely many things within it in so far as human perception, my perception, allows.
" does our current view of time make that impossible"
I think that would prove the opposite if we view time the same way. if one were to look at the universe holistically as one dimension from a fourth then yes all our perceptions and self-determination (in the sense that you're calculating self) would be superfluous? I feel like my current sense of time is atomistic in so far as I cant connect all the points of time together into a coherent body, it simply passes point by point as non divisible portions. However if I somehow were able to atomize all that time into one thing then i'd be able to discern all meaning at one point and thus realize everything making it all worthless to this dimensions self determination. There's nothing to determine. I.e., by establishing something by calculation or research. At that point all things have been realized and there is no determination? This is my amateur opinion. really good question.
the metaphysics section is good for general explanation of what Whitehead means.