My own experience/observation/perception is that one's feet don't really swell up so much as they spread out. the muscles and connective tissue loosen up as one fatigues, the ankles pronate ( i.e., the foot flattens out), and the foot ends up taking up more length and width in the shoe. My own experience is that a pair of good insoles (like Superfeet) will eliminate (or at least minimize) any swelling or spreading out of the feet after a few hours or more of walking or standing.
I'm not a doctor or anything close to it, I'm just passing on what's worked for me over the years. Good quality, close fitting shoes and Superfeet insoles have kept my feet comfy on some very long walks and runs over the years. HTH.