Apache if statement compare two file ages

I want to compare two file ages within .htaccess. If file A is older than file B and REQUEST_URI contains combined.js I want to rewrite url.

RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-l
RewriteCond %{REQUEST_URI} =~ /combined.js/ # && ...? Specific file is older than other specific file.
RewriteRule ^(.+)$ index.php?url=$1 [QSA,L]

How does one check compare file ages in a RewriteCond.