Method in

base/src/main/java/net/time4j/GeneralTimestamp.java:424–446

(
        Timezone tz,
        StartOfDay startOfDay
    )

     * @since   3.8/4.5
     */
    public Moment in(
        Timezone tz,
        StartOfDay startOfDay
    ) {

        PlainTimestamp tsp = (
            (this.cv == null)
            ? this.ca.transform(PlainDate.class).at(this.time)
            : this.cv.transform(PlainDate.class).at(this.time));

        // assuming that deviation will not change much by one day difference (approximation)
        int deviation = startOfDay.getDeviation(tsp.getCalendarDate(), tz.getID());
        int comp = this.time.get(PlainTime.SECOND_OF_DAY).intValue() - deviation;

        if (comp >= 86400) { // happens if sunset is the start of day
            tsp = tsp.minus(1, CalendarUnit.DAYS);
        } else if (comp < 0) { // happens if sunrise is the start of day
            tsp = tsp.plus(1, CalendarUnit.DAYS);
        }

        return tsp.in(tz);

    }

    @Override
    public boolean contains(ChronoElement<?> element) {