So what exactly is the difference between, adjusting pre boil pH and boil pH? What does adjusting at those different times do?Or is it the same thing?
The higher the boil pH the greater the utilization of the hops (and also the greater their harshness). If you want to minimize hop addition mass while maximizing IBU's at the same time, enter the boil at a higher pH.
But if you want to maximize hot break and minimize finings mass, you must hit pH 5.1-5.2 before introducing finings (such as Irish Moss or Whirlfloc).
If you want the very smoothest hop bitterness, and you are willing to use more hops, add acid pre-boil (sufficient to hit 5.1-5.2 pH post boil and cooling). If you want to maximize $$ economy as to both hops and finings expense, add the same qty. of acid with only about 10 minutes remaining in the boil, before finings.