- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$time = 30;
$date = strtotime(date("YmWjis"));
$dote = strtotime(date("YmWjis")) + $time; // ($time is set earlier and is 30 seconds)
echo "wait " . $date = $date - $dote . " seconds until next visit";