Depends. Typically with my internist and gynecologist, I’m seen within a 10 minute window (early or late) of the appointment time. I was especially surprised with the internist when I went back in October (prime flu season, waiting room filled with patients sniffling and wearing masks) and was seen early.
When I broke my wrist, my orthopedist was really on time. My last appointment, I was sick with bronchitis and half-asleep so I wasn’t really paying attention to the fact that I had been in a room for maybe a half-hour with no one checking in. The door opened and a surprised-looking nurse looked at me, checked the chart, and burst out in apologies how I’d been put in the wrong room (and apparently been forgotten about). She and I ran into him in the back hall and she quickly explained to him what had happened. I saw his eyes narrow and he said sternly, “Find out who did this.” I got right into a room, with many apologies from her and the doctor, and was seen quickly.
With some doctors you may find that you may be seen later due to the nature of the practice. With others it’s the doctor him/herself - I have worked for one who could rip through an overfull schedule in four hours (and leave patients feeling that they understood their problems and the treatment suggested) that for another particular doctor it would take at least double that time for the same number of patients and even then you’d worry about when you would be walking out the door that night. One doctor I used to work for would spend an hour talking with “VIP” patients while the other patients squirmed and grouched in the waiting room, but people went to him because of his deserved reputation plus his self-promotion. (Pray you weren’t on the schedule if another MD was on the schedule too.)
I work in ophthalmology and we often get patients sent over from other doctors as emergency walk-ins; typically these are patients who have just suffered a retinal detachment and need rapid evaluation and treatment, though there are other walk-ins as well. A small detachment can be fixed on the spot with a laser, and so the doctor brings the patient back to the laser room and spends a while working on that instead of seeing other patients, or maybe the to-be-lasered patient waits up to an hour while he gets some patients in then delays others for the laser; a more major one involves lots of explanation as to what kind of surgery is going to be scheduled within a couple days, lots of talk about risks, chance of eyesight restoration/other problems, and so on. I remember one day apologizing to a research patient as we’d had three retinal detachments push the schedule so that it was running very late. We got him into a room, and when the doctor took a look at him, this guy had a retinal detachment too! His vision was very poor in that eye so he hadn’t really noticed a change, but it had to be stopped before it started interfering with the parts of his vision that he still had.
I used to work in pediatric cardiology and we had a lot of times when we had way over-stuffed clinic schedules. Before or at the beginning of the school year were bad times (sports clearance, doctor’s note for getting to ride the bus/phys ed restrictions), and I mentioned in another thread that we pretty regularly had teens with musculoskeletal chest pain who had to be crammed onto the schedule as an emergency lest they be in the tiny percent that drop dead first on the basketball court or something, as a result of an actual cardiac problem. There were also the parents who had a kid with basically no residual heart problems but needed yearly visits, and were shocked that they couldn’t get a same-day or same-week (or same-month, often) appointment for a non-urgent yearly visit. (“My child has a heart problem!” I often heard. I never followed up with, “So do all of the other children we see.”) And naturally we had a whole lot of urgent walk-ins sent over by other pediatricians when they heard heart murmurs, especially if there were other symptoms, and these throw the schedule into chaos.
That practice had an awesome young doctor who was very sought-after by other doctors, to the point where they’d stop him in the halls with questions about a possible referral patient. Then he’d run into clinic, late, and spend as long as any family needed to calm fears and answer questions. I had one mother call up looking for a doc for her child, and she asked me which of ours I would recommend. I danced around the question for a bit, talking up each of them, then finally said I thought he was our absolute best. She asked if he ran on time and I gave it to her straight - definitely not, never, but when she was waiting in the waiting room, he would be in a room talking with another family about their child’s heart problem and answering all their questions, and when it was her child’s turn, he would do the same for her. She picked him. I didn’t talk him up much over the others - his clinics were stuffed full anyway, constantly, but word-of-mouth got around too, and people sought him out.