Manage user timezones

index.php

<?php

$timezones = [];
foreach(DateTimeZone::listIdentifiers() as $timezone)
{
    $timezoneWithContinent = explode('/', $timezone);

    if (count($timezoneWithContinent) == 1) {
        // skip UTC
        continue;
    }
    
    $timezones[$timezoneWithContinent[0]][$timezoneWithContinent[1]] = $timezone;
}

// add timezone in select as preference

$date = new DateTime('now', new DateTimeZone($timezones['Europe']['Amsterdam']));

echo $date->format('c'); // 2019-09-16T11:24:37+02:00