- date_diff: documentation ( source)
<?php
$last_partition = new DateTime((1452812400000000 / 1000000) - 1);
$required_partition = new DateTime();
$required_partition->modify('+10 day');
$interval = date_diff($required_partition, $last_partition);
$num_partitions = $interval->format('%a');
echo $num_partitions;