I don't know for sure..just a guess..maybe because everything is still fresh in their minds the very next day..mistakes that need correcting etc?
I don’t know for sure but it seems like it would be a day where there are fewer distractions with no classes and many things on campus closed down. A day to go over what went wrong and what went right the day before while recollections are still fresh.
Travel to USCe would probably keep them from using up all of their practice time (max of 20 hrs/wk & 4 hrs/day) if they waited until Monday.
Would imagine it's a very light "practice". Fifty years ago UF did this and it was as much for the trainers to see who was nicked up and who wasn't (also maybe to see who celebrated to much on game "night"). Think it's as much as a physical check up on everyone as it is a practice. Would imagine there is some film time involved in looking at mistakes that are fresh on everyone's minds from game just played and a first look at your upcoming opponent.