java.time doesn't handle leap seconds very well :(

    jshell> ChronoUnit.SECONDS.between(Instant.parse("1974-01-01T00:00:00Z"), Instant.parse("2024-01-01T00:00:00Z")) % 86400
    $22 ==> 0

astropy gets you the correct answer:

    >>> from astropy.time import Time
    >>> (Time('2024-01-01T00:00:00Z') - Time('1974-01-01T00:00:00Z')).sec % 86400
    24.0

of course astropy is bit specialized and not really something I'd use as general purpose date/time library. But this is one good litmus test for datetimes, feel free to try it with your favorites.