The City Attorney shall expend as much time as necessary to perform the duties of his or her office and in any event shall expend no less than an average of 40 hours per week in the performance of the duties of the office. The City Attorney shall have the right to maintain a private legal practice; provided, that the practice involves no conflict of interest with his or her representation of city as City Attorney; provided further, however, that the maintenance of the practice does not interfere with his or her performance of his or her duties as City Attorney; and provided further, however, in conducting the practice he or she does not become engaged in trials of an adversary nature.
(`78 Code, § 2.16.090.)