xmlgregoriancalendar hashcode does not handle milliseconds

Question

I am trying to hash my object:

protected XMLGregorianCalendar startTime;

value of getStartTime() is 2018-06-21T12:04:10.000Z

The hashCode method at the bottom from XMLGregorianCalendar does not handle milliseconds, so I will never get a unique hashCode even when I use a startTime with different value for milliseconds like 2018-06-21T12:04:10.111Z

Both 2018-06-21T12:04:10.000Z and 2018-06-21T12:04:10.111Z result in the same hashCode unless I change the seconds, minutes, hour, etc etc. I need it to also take into account the milliseconds.

Is there a different hashCode() method that will handle this? How can I accomplish this?

   public int hashCode() {

        // Following two dates compare to EQUALS since in different timezones.
        // 2000-01-15T12:00:00-05:00 == 2000-01-15T13:00:00-04:00
        //
        // Must ensure both instances generate same hashcode by normalizing
        // this to UTC timezone.
        int timezone = getTimezone();
        if (timezone == DatatypeConstants.FIELD_UNDEFINED) {
            timezone = 0;
        }
        XMLGregorianCalendar gc = this;
        if (timezone != 0) {
            gc = this.normalize();
        }
        return gc.getYear()
                + gc.getMonth()
                + gc.getDay()
                + gc.getHour()
                + gc.getMinute()
                + gc.getSecond(); //Where's milliseconds???
    }