Ok...you're right, but this should work:
<?php
switch($x)
{
case ($post['regdate']+(60*60*24*30) <= TIME_NOW):
echo '<div class="postbit-time-1month">1 month on MMH</div>';
break;
case ($post['regdate']+(60*60*24*62) <= TIME_NOW):
echo '<div class="postbit-time-2month">2 months on MMH</div>';
break;
case ($post['regdate']+(60*60*24*182) <= TIME_NOW):
echo '<div class="postbit-time-halfyear">1/2 year on MMH</div>';
break;
case ($post['regdate']+(60*60*24*365) <= TIME_NOW):
echo '<div class="postbit-time-year">1 year on MMH</div>';
break;
default:
echo '';
break;
}
echo $x;
?>