如何根据URL检查文件创建日期？

I have an URL to a XML file, is there any posibility to get its creation date ?

NO.
because its a web url you possibly cannot get more information that what the web server exposes

Yes can get a file information using CURL curl_getinfo without having to return the entire body

Example

$curl = curl_init('URL_TO_XML');
curl_setopt($curl, CURLOPT_NOBODY, true);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_FILETIME, true);
$result = curl_exec($curl);
if ($result === false) {
    die (curl_error($curl)); 
}
$timestamp = curl_getinfo($curl, CURLINFO_FILETIME);
if ($timestamp != -1) { 
    echo date("Y-m-d H:i:s", $timestamp);
} 

You can do it that way

Uri myUri = new Uri(url);

// Creates an HttpWebRequest for the specified URL. 
HttpWebRequest myHttpWebRequest = (HttpWebRequest)WebRequest.Create(myUri); 
HttpWebResponse myHttpWebResponse = (HttpWebResponse)myHttpWebRequest.GetResponse();

DateTime today = DateTime.Now;
// Uses the LastModified property to compare with today's date.
if (DateTime.Compare(today,myHttpWebResponse.LastModified) == 0)
    Console.WriteLine("
The requested URI entity was modified today");
else
    if (DateTime.Compare(today,myHttpWebResponse.LastModified) == 1)
        Console.WriteLine("
The requested URI was last modified on:{0}",
                        myHttpWebResponse.LastModified);
    // Releases the resources of the response.

myHttpWebResponse.Close();