a question of import, revealing much of human frailty, arrogance, and your friend's secrets - their most personal weltanschauung
my sheets are (not by me) changed on Friday afternoon, in honor of the oncoming Sabbath. The Sabbath begins according to tradition on Friday night (every day begins at nightfall) since god, the Lebowski dude created the world, per Genesis, it was done in this order - "and there was evening, then there was day."
so I figured that an offer of a day of regularized rest deserved clean sheets on the eve of its conception.
some of you who agree with view may prefer Saturday afternoon/evening, since your sabbath occurs primarily on Sunday, and in many parts of the world sabbath is coincidentally purposed for laundry anyway.
that said, you may very well change your sheets on whatever is laundry day in your mansion or dorm room. However, I defy you atheists to deny that you think when slipping in between two fresh sheets, "there is a god"