<?php
$s = 84600; // 23.5 h in seconds
$s += (60*60*24)*38; // add 38 days in seconds
$d = (new \DateTime())->modify("-".$s."seconds");
echo (new \DateTime())->diff($d)->format("%a days %h:%I"), PHP_EOL;
$d = (new \DateTime())->sub(new DateInterval('PT'.$s.'S'));
echo (new \DateTime())->diff($d)->format("%a days %h:%I"), PHP_EOL;