$day = 'Thursday';
$i = 0;
$o_date = new DateTime("2012-09-12 20:56:43 +18 hours");
$date = date_format($o_date, 'l');
$full = date_format($o_date, 'd-m-Y');
if($day!=$date) {
    $date = new DateTime($date . " +1 days");
    $i++;
}
$order_day = new DateTime($full . " +".$i." days");$order_day = date_format($order_day, 'D, d M');
return $order_day;

$day = 'Thursday';
$day_names = array('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday');
$day_num = array_search($day, $day_names);
$o_date = new DateTime("2012-09-12 20:56:43 +18 hours");
$o_day_num = $o_date->format('w');
$day_diff = ($day_num - $o_day_num) % 7;
if ($day_diff == 0) { $day_diff = 7; }
$order_day = clone $o_date;
$order_day->add(new DateInterval("P".$day_diff."D"));

<?php
$day = 'Thursday';
$i = 0;

// Order Date
$o_date = new DateTime("2012-09-12 20:56:43 +18");
$date = $o_date->format('l');

while($day!==$date) {
  $date = $o_date->add(new DateInterval('P1D'))->format('l');
  $i++;
}
$order_day = $o_date->format('D, d M');