Best selection will be Thursday night (the evening before the show starts) at the Golden Manor motel (where the crew stays). I can't speculate about how much will be left for the show opening because I have no idea of how many and what models Dan will send. I've been to a few shows, and will state that any uncommon models (like mudder-handled knives) that are in limited supply (say only 4 or 5) WILL sell out the night before. Dog Fathers or Muks, which are in high demand and haven't been available the last couple shows, would sell out much faster than SoDs or Mutts. Scrap Yard doesn't usually send as many knives to Knob Creek as SR or BC, so the sooner you get to the tables, the better your selection.
I don't know where you're traveling from, but if your primary goal is to buy knives, I'd recommend making an effort to be at the motel on Thursday. If you're mainly just coming for the show, there'll still be knives for sale as late as Sunday, but they'll have been picked over. Friday morning should be good, but not nearly as good as Thursday night; Friday evening won't be as good as Friday morning, but would still be better than Saturday.