I am not a dermatologist, nor do I play one on TV, but I would hazard a guess that after 12 hours, your skin hasn't completely recovered from a serious exfoliation. Since the process of exfoliation involves removing dead skin cells, one could infer that if the skin hasn't had sufficient time to replenish those cells, that a premature shave would remove cells from a lower layer, thus causing irritation.
As for the shave simply not being as close, I might venture another guess that there is simply less surface area on the hair to absorb moisture, which is the basic goal of any prep routine. If this is the case, then one might assume that the whisker is still quite a bit tougher than one would want it to be for an optimal shave.
So, unrecovered skin and less well-prepped whiskers.
That's my guess...
Portland, Oregon, USA
[I]Any statements in the above post should be used for entertainment purposes only, and should not be considered actual information, or used for investment purposes.[/I]