How long does it take to amend the National List? A substance may be removed from consideration at any step of the process. However, steps 1 to 4 are usually completed for all petitions within 12 to 18 months of the filing date, with a minimum of about 145 days needed. Once a recommendation to list a petitioned substance reaches the NOP, it technically enters the rulemaking process (Step 5). The first amendments to the National List became final in the Fall of 2003, over three years for some of the petitions filed. The shortest time for a petition to make it on the National List was approximately two years.