// Created on savesnippets.com · https://savesnippets.com/7dwy6bPNIGlMsT
<?php
function formatDuration(int $seconds): string {
    if ($seconds < 0) return '-' . formatDuration(-$seconds);
    if ($seconds === 0) return '0s';

    $units = ['d' => 86400, 'h' => 3600, 'm' => 60, 's' => 1];
    $parts = [];
    foreach ($units as $label => $size) {
        if ($seconds >= $size) {
            $n        = intdiv($seconds, $size);
            $seconds %= $size;
            $parts[]  = $n . $label;
        }
    }
    return implode(' ', $parts);
}

echo formatDuration(75);          // 1m 15s
echo formatDuration(3725);        // 1h 2m 5s
echo formatDuration(90000);       // 1d 1h