This is what I have done in the past. Ask the receptionist how long your scheduled appointment is. After that length of time has exceeded your appointment time, inform the receptionist that this is all the time you have allotted for the doctor and you will call them to reschedule. I can understand them running late occasionally, but this is the practice.
User Detail :
Name : Buddy B., Gender : M, Sexual Orientation : Straight, Race : White/Caucasian, Age : 60, City : Glen Allen, State : VA, Country : United States, Occupation : IT Manager, Education level : Technical School, Social class : Upper class,