<?php
$time=strtotime('18:30:00');

echo $time."\n";

echo date("g:i a",$time);

$time=strtotime('6:30 pm');
echo "\n\n".$time."\n";

echo date("H:i:s",$time);
?>

1354732200
6:30 pm

1354732200
18:30:00