I think this is the correct answer, just change Europe/Stockholm
to the users time-zone.
$dateTime = new \DateTime(
'now',
new \DateTimeZone('Europe/Stockholm')
);
$day = $dateTime->format('N');
ISO-8601 numeric representation of the day of the week (added in PHP 5.1.0) 1 (for Monday) through 7 (for Sunday)
http://php.net/manual/en/function.date.php
For a list of supported time-zones, see http://php.net/manual/en/timezones.php