<?php
$dir = Mage::getBaseDir().DS.'var'.DS;
$fileName = $dir.'real_static_categories.phtml';

if(!file_exists($fileName)||(filemtime($fileName)&&(time()-filemtime($fileName)>7200))){
    $text=Mage::app()->getLayout()->createBlock('catalog/product_list')->setTemplate('catalog/product/productcarousel/carouselblocks/categories.phtml')->toHtml();
    $file=fopen($fileName,'w');
    fwrite($file,$text);
    fclose($file);
}
$file=fopen($fileName,'r');
echo fread($file,filesize($fileName));
fclose($file);

?>