By R. M. Bottger. The Social Security Administration will tell you that it takes an average of 120 days to make a decision on your Social Security and/or Supplemental Security Income disability claim. However, this is not the whole story.ven the people that understood that the 120 days was an average were still confused about how long their claims were going to take. Many thought that their cases would take 120 days give or take a few days. In reality, the amount of time that it takes to make a decision varies greatly from case to case.