- date_create: documentation ( source)
- date: documentation ( source)
- max: documentation ( source)
- min: documentation ( source)
<?php
$daysAgo = 3;
$datetime = date('YmdHis');
print max(date_create($datetime)->modify('- '.$daysAgo.' days')->format('YmdHis'), '20140509182257');
print min($datetime, '20140509182257');