90% of the time I will know when my MRI will be before I even leave the office. The other 10% my wife will have to call where the MRI is to be done and gets the date and time then. If you doctor said it was urgent and the receptionist said it could take up to 4 weeks, I would find another doctor. On average I would say, I have to wait 2 to 3 weeks for a routine MRI. For one that is suppose to be urgent it should be less than a week.
Two hours. That was when I has a suspected aneurysm.