- preg_split: documentation ( source)
- strtotime: documentation ( source)
<?php
$fecha = "20/04/2015 18:11:54";
list($d, $M, $y, $h, $m, $s) = preg_split("/[\s,\/:]+/",$fecha);
echo strtotime("$d $M $y $h:$m:$s");
echo "<br>";
echo strtotime("2015-04-20") - '1429571959';
echo '<br>';
echo strtotime("20/04/2015 18:11:54") - '1429571959';