> The Unix timestamp that this function returns does not contain information about time zones. In order to do calculations with date/time information, you should use the more capable DateTimeImmutable.
important - does not contain
<?php
date_default_timezone_set('Europe/Berlin');
// .... a lot of code
echo $a = strtotime('yesterday 00:00');
// in $a hour = 23:00:00 and you may not know about it
// https://onlinephp.io/c/ef696
// use DateTimeImmutable