Agreed, that size and density is what matters. It also matters how salty your brine is. The saltier the brine the less time you will want it submerged. When it comes right down to it though it is going to be personal preference based on trial and error. I brine chicken breasts 2-3 hours max. Any more and I find the texture really gross. Something thicker and larger like a pork loin will allow for a longer brine.