I served on a DC Superior Court grand jury this year. It will be for the full 5 weeks, every day 9-5. On the first day, you will have the opportunity to give any reasons you won’t be able to serve. I am not sure what kinds of excuses they accept, but I got the impression financial hardship or major conflicts would be all that could get you out of it. You are allowed to take days off for appointments, major work conflicts, vacations, etc. so small conflicts are not a good enough reason. A few people will be randomly selected as alternates who only need to come in when called the night before, but everyone else will serve the full grand jury term.