How to get next day end of day date time from given Instant ? (Java)

If you want the actual midnight (00:00), you can use:

instant.plus(1, ChronoUnit.DAYS).truncatedTo(ChronoUnit.DAYS);

Otherwise, another solution would be:

LocalDateTime ldt1 = LocalDateTime.ofInstant(instant.plus(1, ChronoUnit.DAYS), ZoneId.systemDefault());

ldt1 = ldt1
        .withHour(23)
        .withMinute(59)
        .withSecond(59);

Instant result = ldt1.atZone(ZoneId.systemDefault()).toInstant();

One way is converting Instant to ZonedDateTime with UTC timezone and modify the date as per requirement and then convert it back

Midday :

Instant result = instant.atOffset(ZoneOffset.UTC)
                        .plusDays(1).with(LocalTime.of(11,59,59,instant.getNano()))
                        .toInstant();

End of day :

Instant result = instant.atOffset(ZoneOffset.UTC)
                        .plusDays(1).with(LocalTime.of(23,59,59,instant.getNano()))
                        .toInstant();