Dapat masukan dari pingdom katanya sebagian file memiliki waktu yang terlalu singkat makanya harus diperpanjang, kurang lebih triknya begini..
pakai htacces:
## EXPIRES CACHING ##   
<IfModule mod_expires.c>    
ExpiresActive On    
ExpiresByType image/jpg "access 1 year"    
ExpiresByType image/jpeg "access 1 year"    
ExpiresByType image/gif "access 1 year"    
ExpiresByType image/png "access 1 year"    
ExpiresByType text/css "access 1 month"    
ExpiresByType text/html "access 1 month"    
ExpiresByType application/pdf "access 1 month"    
ExpiresByType text/x-javascript "access 1 month"    
ExpiresByType application/x-shockwave-flash "access 1 month"    
ExpiresByType image/x-icon "access 1 year"    
ExpiresDefault "access 1 month"    
</IfModule>    
## EXPIRES CACHING ##