No, unless the computer's time settings were changed to use as the timezone "UTC" or "Reykjavik", where the offset from UTC is zero year round, and there's no daylight saving time period. As Raccoon was saying, $gmt(N) for a specific N should return the same as UTC(N), a time not offset by daylight, and not messing around with leap seconds.
$gmt(0) should report the same thing for everyone, as it currently does. But it also should report the same thing all year long, instead of adjusting its results based on the current value of $daylight.
For USA Central, $asctime(0) reports "Wed Dec 31 18:00:00 1969", and a different time for everyone in a different timezone. $gmt(0) for everyone should be "Thu Jan 01 00:00:00 1970"
As my alias in the prior post was showing, when "N" is a multiple of 86400 it should return midnite. Any modulo is the hr:min:secs since midnight.
In effect, the HH:nn:ss portion of the display should be the same as
//echo -a $duration( $calc(N % 86400) ,3)
And makes most of the alias in the prior example simpler:
//echo -a $duration( $calc($calc($calc( 1547987696 + 86400*181)) % 86400) ,3)
//echo -a $duration( $calc($calc($calc( 1547987696 + 86400*0 )) % 86400) ,3)