Is it possible within a PIX 515e ver 6.3(3) (Yea, I know it's old) to set time limits on certain access rules? I am looking to limit FTP access to a limited window.
Thus, your current version on PIX will not be able to use timebased ACLs. However, you can upgrade your PIX to 7.x code inorder to use it. Here is a link which explains about requirements/procedure on howto upgrade PIX to 7.0 code-