Please don't take this as defending their actions. In the age of fewer doctors, over booking, and do more with less, you will find this continuing. My best advice is to make early appointments. The earlier in the day, the less the doctor is behind.
This is what I do with my Pain Management Dr...They have a bulletin board in the lobby that shows how far behind the Dr is. On average it's 45 minutes to 1 hour. I finally figured out if I can work it out to be one of the first in the am it's not bad. Heard rumors the clinic schedules patients at 10 minute intervals to make the Corporate big wigs happy. That's how they get so far behind. I have to see my Pain Dr.once every 3 months or I can't get my oxycodone and I won't put myself through that again. If you miss your appointment you DON'T get back in for 3 months....they will tell you to go to urgent care. Dr is a great guy but the Clinic is run like a cash cow so customer service means nothing. I have walked out on my regular Dr. before after an hour. I guess to answer your question ...it depends how bad you need to see the Doc as to how long you wait. Good luck