Male jurors are expected to wear collar, tie, and coat while female jurors pantsuit, skirt or dress ... no jeans/shorts allowed.
Depending on how many cases are going that particular day, you could be at the courthouse until p.m. - p.m. When you are serving on a case, the hours are approximately a.m. - p.m. (depending on the judge).
You might be excused altogether, or your date may be deferred (rescheduled). These accepted excuses will depend on the court that called you for jury duty. You must ask to be excused. This generally involves filling out an affidavit or calling the court.