select by time from mongodb by using php error -

i trying query mongodb using php, database looks this

{     "_id" : objectid("55892817d4302e281b8b4567"),     "subject" : "report",     "createdat" : isodate("2015-06-23t09:34:15z"),     "processedat" : isodate("2015-07-23t09:34:15z"),     "testnumber" : 10 } 

and query is:

$procinmins = 60; $anchor = new \datetime('now', new \datetimezone('utc'));  // $anchor->sub(new \dateinterval('pt' . $procinmins . 'm')); $query = array( "subject" => "report", "processedat" => array( '$gt' => $anchor)); $cursor = $collection->find($query); 

and returns cursor count 0, tried

$query = array( "subject" => "processoverflowsmslogcommandtest report", "testnumber" => array('$gt'=>3) ); 

in case compare testnumber field , returns 1 result, correct. think there's wrong date, have no idea how fix this. thanks