- var_dump: documentation ( source)
- date_default_timezone_set: documentation ( source)
<?php
date_default_timezone_set('America/New_York');
$InitialDateTime = DateTime::createFromFormat('U', '1409611999');
$firstDayofWeek = clone $InitialDateTime;
$firstDayofWeek->modify('Monday This Week');
$lastDayofWeek = clone $InitialDateTime;
$lastDayofWeek->modify('Saturday This Week');
var_dump($initialDateTime, $firstDayofWeek, $lastDayofWeek);