The actual visit to the doctor in the doctors office to get checked over and have a checkup is around 5 minutes to 30 minutes depending on what the doctor is checking you out for.
Most of my doctors visits require about 20 minutes in the waiting room and then another 10 to 15 minutes in the office of the doctors.
It's usually the waiting room time that takes longer than the actual check up at the doctors office.
But if you go to urgent care or the emergency room then those visits can take as long as 3 hours from start to finish and sometimes longer if you're admitted to the hospital for a stay.