My doctor's office has a sign that says if you having been waiting 15 minutes past your appointment to let them know. I rarely have to wait even the 15 minutes. I understand emergencies, especially at a surgeon or cardiologist, but I will not go to a doctor who overbooks and makes me sit well past my appointment time. Many years ago I had a GP who overbooked so badly that they told you to call before coming to see how far behind they were. I changed doctor's very quickly. My time is as valuable as the doctor's.