Paul: Conversion, Commission, and Chronology

When did Paul get his "commission" to go to the Gentiles? Was it on the Damascus Road (e.g. Gal. 1.13-14; Acts 26:14-15) or a subsequent relevation, or then again was it something that only became clearer to him later on in his ministry (Acts 22.17-18)? If this call only came into perspective later on, did Paul consider his period of time in Arabia as part of his call to go to the Gentiles (Gal. 1.17). One of our HTC students, David Kirk, has a good run down on this.