Update time without NTP with PHP

date_update.php

<?php
/**
 * Little script to update date based on SO answer here: https://askubuntu.com/a/655528/158714
 * but with more security in mind (as that answer just feeds the output right into bash)
 *
 * Useful for little VMs when NTP is blocked and you put VMs into saved state regularly/
 *
 * Run via cron as root or other privileged user.
 *
 * Robert Dundon
 * (C) 2017 BH Media Group, Inc. (I wrote this at work, for work)
 */

//Site to get the Date header from
$url = 'http://www.example.com';

//Get the headers
$header_lines = get_headers($url);

//Parse headers accordingly
$headers = [];
foreach ($header_lines as $header_line) {
        $header_datum = explode(': ',$header_line);
        $key = $header_datum[0];
        $value = $header_datum[1];
        $headers[$key] = $value;
}

// Convert string of header to timestamp (helps sanitize the given header data), and convert it to ISO 8601
$new_date = date('c',strtotime($headers['Date']));

// Then set the date
exec("date -s $new_date");