Since Dwight Lincoln Hammond, Jr., and his son, Steven Dwight Hammond already served their original sentence and were released from prison, we see no reason for them to have to serve an additional length of time.
The original judge in the trial (Judge Hogan) overruled the minimum terrorist sentence that is now being used as the justification for their reimprisonment. He wrote that if the full five years were required, it would be a violation of the 8th amendment (cruel and unusual punishment).