It depends on the doctor, but routine hearing tests typically take about 20-30 minutes. This involves an interview, examination, which determines what type of hearing loss you or your loved one has, and recommendations for treatment options. Most times, the recommended treatment option is a hearing aid.
The New York Hearing Doctors is a great resource that outlines the whole hearing test process from start to finish. Not only will it hep you to prepare, but it will also provide you with a better understanding of the test so you will know what to expect.