I've got a double whammy, ADHD and medical issues. But my coping mechanism for ADHD scheduling is calendar entries with multiple reminders. It's hard to learn new habits, but I wouldn't let another ADHD person use it as an excuse more than a couple times before I just moved on. As for medical issues, they're generally in the morning and I usually plan afternoon or later so if I have to cancel there is a bit of advance notice.