Cache\Adapter\Common\CacheItem::expiresAt PHP Method

    public function expiresAt($expiration)
    {
        if ($expiration instanceof \DateTimeInterface) {
            $this->expirationDate = clone $expiration;
        } else {
            $this->expirationDate = $expiration;
        }
        return $this;
    }

 /**
  * Store a response generated by a request.
  *
  * @param Request $request
  * @param Response $response
  * @param integer $ttl
  */
 public function cache(Request $request, Response $response, $ttl = null)
 {
     // only cache GET and HEAD requests
     if (!in_array($request->getMethod(), array('GET', 'HEAD'))) {
         return;
     }
     // respect Cache-Control: no-cache
     if ($request->isNoCache()) {
         return;
     }
     // skip already cached response
     if ($response->headers->has('X-ServerCache-Key')) {
         return;
     }
     // set cache lifetime
     if (is_null($ttl)) {
         $ttl = $this->defaultTtl;
     }
     $expirationDate = date_create('NOW + ' . $ttl . ' seconds');
     // save cache item
     $key = $this->getCacheKey($request);
     $metadataReponse = new MetadataResponse($response, array("expirationDate" => $expirationDate));
     $item = new CacheItem($key, true, $metadataReponse);
     $item->expiresAt($expirationDate);
     $this->cache->save($item);
 }