A half hour or hour brine is not going to penetrate the whole chicken. It's going to give it a light version of the flavor, intentionally. The longer period will soak all the way through, generally the timing has to do not only with how much you want it to absorb but how dense the flesh is, which is why a pork chop needs longer, as does, say, a corned beef brisket.
I will say re Cooks Illustrated that after my first year brining a turkey, I loved their method but I cut the intensity of the brine literally in half the next year. Too salty, too much of everything.