Period of Adhoc promotion to be considered for promotion

Want a advice for my query My friend was promoted to the post Asst Conservator of Forests , IN FOREST DEPT in 2007 on adhoc basis and his promotion was regularised in October 2011 by state public service DPC. NOW HE WANTS TO SEEK FOR NEXT PROMOTION AS DY. CONSERVATOR OF FORESTS FOR WHICH AS PER RECRUITMENT RULES ONE MUST HAVE SERVED AS ASST. CONSERVATOR OF FORESTS ON REGULAR BASIS FOR MINIMUM 6 YES. CAN CLAIM FOR THE PERIOD SERVED ON ADHOC PROMOTION ( 2007 TO 2011)FOR HIS NEXT PROMOTION? IF YES THEN UNDER WHICH RULES AND ANY ORDERS PASSED BY COURT IN SUCH CASES