How long would you wait in a Doctor's waiting room before leaving? Keep in mind that the apppointment is not an emergency, just a standard follow up...
I found out mine is 70 minutes. Watching people sign in after me, get seen before me and leave while I was waiting is infuriating.
After 1 hour and 10 minutes, I told the receptionist I was leaving and I'll call to make another appointment. Wouldn't you know that they called me 5 minutes later to see if I was still in the building because they just called me in.