the day off after quarterfinals will help a ton for the winner of the USC/Ohio St match that'll be a really physical battle and help offset any fatigue. I don't see it being that big an issue unless weather balloons into the mid 80s or 90s.
back when the tournament used to only have a day off after rnd of 16 then play quarter semis finals back to back to back did we worry so much about fatigue. these guys are pretty darn fit and have full training staffs with them. they get pedialyte, IV fluids, you name it to stay hydrated.
That's a relief. According to some posts, they all ride in the back of the van, stop at a subway on the way to the courts, play their matches and then climb back in the van for a 8-hour ride home.