$datetime = '2012-03-24 17:45:12';
$time = date_format($datetime, 'g:i A');
echo $time;

$date = new DateTime("2012-03-24 17:45:12");
echo $date->format("g:i A");

$datetime = date_create('2012-03-24 17:45:12');
$time = date_format($datetime, 'g:i A');
echo $time;