The frequency with which you need to see a psychiatrist on an outpatient basis will depend on whether you are just starting on medications or have already been on them.
The initial session with a psychiatrist, which will last around an hour, mostly gives the psychiatrist a chance to get a good history of your illness and then talk to you about what medications are available to treat your OCD.
The psychiatrist will then give you a prescription for a medication and will probably want to see you two to three weeks later to be sure that there are no complications.
Future sessions will probably be monthly or bimonthly for the first six months and will last approximately fifteen minutes each, just to see how the medication is working and to make any necessary adjustments. After you have been stabilized on a medication, you may meet with the psychiatrist every four to six months for prescription refills and any minor changes that may be needed.
Of course, if there are ever any complications, you may call and make an appointment as needed.