I had grand jury duty in NY, so it sounds different in NJ. Once I was selected for the grand jury, I had to be there everyday for a month - no more, no less. It isn't the same as jury duty. In grand jury duty, you are listening to cases and deciding if the defendant should be indicted or not. If yes, then they go to trial. We sat there for a month, and sometimes cases came in, sometimes nothing all day. Sometimes several in a day. It was boring, but when there was a case, it was actually pretty interesting. Bring a book or something else to do for the downtime. If you have to go one day for 9 weeks, then the duty is obviously different, but the responsibilities are the same.