Clothing weblog Put This On recommend doing all your shoe-shopping after you've walked around for a few hours, to ensure you get the best-fitting shoes.
Photo by Marc Berry Reid.
Put This On explains:
Try doing your shoe shopping after 3pm. Feet swell after a bit of walking, so by trying on shoes in the late afternoon, you'll ensure that you'll get the most comfortable fit.
This is of course only true if you wake up in the morning and have done a bit of walking. If you don't wake up until the afternoon, then you should just finish grad school.
It's unlikely your feet are going to swell a whole shoe size, but if you're on the verge of one size, this could easily be the difference between comfortable shoes and shoes that make your feet feel constricted.
Try Doing Your Shoe Shopping After 3pm [Put This On]