As someone with 36 direct reports, I tell them I need to know ASAP. My techs (I work in a pharmacy) have every other weekend off as well as one day every week, so I expect them to schedule their appointments on their days off. If it's an emergency or they have to work around a doctor's office's weird hours, I need as much notice as possible, as I need to get coverage so that my nursing home residents get their meds in a timely manner. And, they need to have the PTO time available to cover the time off work. No PTO time, no time off work. If I get no notice and someone lets me know that day they they will either be off or working less than 6 hours (per company policy) it's unexcused. Even if they have a note. Dr's notes only excuse you after 5 unexcused absences per year, and 7 is termination.
So, technically they have to give me at least a day's notice to not get an unexcused absence point. But if they make a habit of last-minute notice, they will get counseled and written up.