$arr = array(
array(
'name'=>'a',
'date'=>'2012-10-21 18:00:00'
),
array(
'name'=>'x',
'date'=>'2013-10-21 18:00:00'
),
array(
'name'=>'d',
'date'=>'2011-10-21 18:00:00'
)
);
foreach($arr as $r) $t[] = $r['date'];
array_multisort($t, $arr);
array_multisort($t, SORT_DESC, $arr);
print_r($arr);
