<?php
 
// your code goes here
$json = '{
    "items": [
        {
            "id": "8498",
            "title": "Item 2",
            "pubdate": "2015-03-01 10:29:00 +0000"
        },
        {
            "id": "8497",
            "title": "Item 1",
            "pubdate": "2015-03-01 16:29:00 +0000"
        }
    ]
}';
 
$arr = json_decode($json, true);
 
$items = $arr['items'];
 
usort($items, function($a, $b) {
    if ($a['pubdate'] == $b['pubdate'])
        return $a['id'] < $b['id'];
 
    return ($a['pubdate'] < $b['pubdate']) ? -1 : 1;
});
 
print_r($items);

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