When I get new glasses, I'm usually completely used to them in a day.

I got one pair, however, that had a place on one of the lenses that was not correct. (They told me what happened at the time, but I can't remember.) I kept them a week, and they never got better ... I still knew something was just "off". I took them back, they found the spot, and made me a new lens. Then everything was fine in about a day.