gistfile1.php

<?php

$startTime = strtotime('-1 hours');
$endTime = $startTime + 3600;

$result = $client->getMetricStatistics(array(
	'MetricName' => 'Latency',
	'Namespace'  => 'AWS/ELB',
	'StartTime'  => $startTime,
	'EndTime'    => $endTime,
	'Period'     => 300,
	'Statistics' => array('Average'),
));

print_r($result['Datapoints']);