DH and I are both teachers and have this policy and I wonder if it's the same in other jobs.
If I need a day off for illness I have to ring school between 7:30 and 8am. I appreciate that schools need to know as early as possible if staff aren't going to be in, and this works fine in the situation that you wake up ill in the morning. DH came home ill yesterday and last night let his head of department know he wouldn't be in today and cobbled together some cover work but he still has to be up to ring the absence line.
AIBU to think that if its obvious the previous day that you're going to be off ill the next day there should be another way of letting them know as often having a good sleep can make you feel much better?