Reply #2: Here is a description of grand juries terms, extensions [View All]

Grand jury's term
Federal grand juries are of two types--regular and special. Regular grand juries sit for a basic term of 18 months, but that term can be extended up to another 6 months, which means their total possible term is 24 months. Special grand juries sit for 18 months, but their term can be extended for up to another 18 months; a court can extend a special grand jury's term for 6 months, and can enter up to three such extensions, totaling 18 months.

http://www.udayton.edu/~grandjur/fedj/fedj.htm#Grand%20jurys%20term

Edited to add info on regular and special grand juries:

There are two kinds of federal grand juries: Regular federal grand juries and special federal grand juries. Regular federal grand juries tend to spend their time hearing evidence and considering indictments submitted to them by a prosecutor. They spend the bulk of their time deciding, therefore, whether probable cause exists to return a set of proposed charges against the defendants names therein. Special federal grand juries were created in 1970 specifically to investigate organized crime. They, too, consider whether indictments should be returned against certain persons, but special grand juries also devote a great deal of their time to investigating possible criminal activity.