The judges try to seat their juries in the morning, therefore, if you are not seated on a case, you are normally released in the early afternoon. If you are a juror on a particular trial, you should plan on being at the courthouse until about 5 p.m.
The average trial length is one day in District Court, one day in Probate Court and three days in Circuit Court. Occasionally a case will last longer. The judge will inform you of the expected length of the case during jury selection.