I do it a day and sometimes day of, usually around when I'm checking in for my flight. I've still received my room requests without issue. Part of it is just conflating checking in at Disney with what "check in" means almost anywhere else, even though those things are different. I don't want to accidentally commit myself in a way that I can't undo. And even though that's not how Disney check-in seems to work, I still just wait until I'm absolutely sure that nothing is going to change about my reservation.