- date_default_timezone_set: documentation ( source)
<?php
date_default_timezone_set('Asia/Tehran');
$date1 = new \DateTime('2019-08-21 12:47:24');
$date2 = new \DateTime('2019-09-24 11:47:24');
//$date2 = new \DateTime('2019-08-21 12:47:24');
$diff = $date1->diff($date2);
$date3 = new \DateTime('@' . $date1->format('U'));
$date4 = new \DateTime('@' . ($date2->format('U')-3600)); //Sun 22 set, 0.00 a.m, when local clocks were set backward 1 hour
$diff2 = $date3->diff($date4);
if ($diff->h < 0) {
echo $diff->format('%R%a Total number of days as a result of a DateTime::diff() or (unknown) otherwise %d days not already covered by the month Time = %H:%I:%S') . PHP_EOL;
echo $diff2->format('%R%a Total number of days as a result of a DateTime::diff() or (unknown) otherwise %d days not already covered by the month Time = %H:%I:%S') . PHP_EOL;
}