- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$date_now_start = date('Y-m-d H:i:s');
echo date('Y-m-d', strtotime('yesterday', strtotime($date_now_start)));
$date_end = date('Y-m-d ', strtotime("yesterday"));
echo date('Y-m-d', strtotime($date_end));