it has been my experieince that (early) monday mornings are generally busy at las with such short flights to oak, sfo, lax, sna & lax as folks will go straight to work (ugh) (and also the wn terminal for the flights [aka the stripper specials) to lax, sna & san] and if it also happens to be at the end of a convention w/e, then that's gonna add to the crowds as well.
n.b. i leave on sunday afternoons or the monday of a holiday w/e to avoid just this