- time: documentation ( source)
- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$one_year_ago = date('Y-m-d 0:00', strtotime("-1 year", time()));
$retry_after_date = new DateTime($one_year_ago);
echo 'start::'.$retry_after_date->format('Y-m-d H:i');
for ($i=5; $i < 50; $i+=5) {
// $retry_after_date = DateAdd("n", 5, RetryAfterDate)
$retry_after_date->add(new DateInterval('PT' . $i. 'M'));
echo "\n".$retry_after_date->format('Y-m-d H:i');
}