How to sort PHP multidimensional array by timestamp

sort_multidimensional_array_by_time.php

// Feeds array with title and time
$feeds = array(
    array(
        'title'  => 'Some Feeds.',
        'time'  => '2015-03-31 13:06:00'
    ),
    array(
        'title'  => 'And another.',
        'time'  => '2015-03-23 13:06:00'
    ),
    array(
        'title'  => 'Another Feed.',
        'time'  => '2015-03-27 13:06:00'
    ),
    array(
        'title'  => 'And one more feed.',
        'time'  => '2015-03-20 13:06:00'
    ),
    array(
        'title'  => 'And one more feed.',
        'time'  => '2015-03-25 13:06:00'
    )
);

// Sorting array by time (DESC ORDER)
usort($feeds, function($firstItem, $secondItem) {
        $timeStamp1 = strtotime($firstItem['time']);
        $timeStamp2 = strtotime($secondItem['time']);
        return $timeStamp2 - $timeStamp1;
    });
var_dump($feeds);

// Sorting array by time (ASC ORDER)
usort($feeds, function($firstItem, $secondItem) {
        $timeStamp1 = strtotime($firstItem['time']);
        $timeStamp2 = strtotime($secondItem['time']);
        return $timeStamp1 - $timeStamp2;
    });
var_dump($feeds);