RandomShiftOnDate.java

private static Random random = new Random();
private static int MIN = 60 * 1000;
private static Calendar cal = Calendar.getInstance();

public static Date randomShiftOnDate(Date someDate) {        
    int randomValue = (random.nextInt(61) - 30) * MIN; // +/- 30 min.
    long time = someDate.getTime() + randomValue;        
    Date result;
    synchronized (cal) {
      result = cal.setTimeInMillis(time).getTime();
    }
    return result;
}