Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Shared/TimeZone.php
public static function setTimeZone($timezone)
    {
        if (self::validateTimezone($timezone)) {
            self::$timezone = $timezone;

            return true;
        }

        return false;
    }
public static function setTimeZone($timezone)
    {
        if (self::validateTimezone($timezone)) {
            self::$timezone = $timezone;

            return true;
        }

        return false;
    }
Set the Default Timezone used for date/time conversions.

@param string $timezone Time zone (e.g. 'Europe/London')

@return bool Success or failure