that's the browser cache time, not the time it is cached on the server. You don't really want the browser to cache pages - if you correct even a typo in a post, the browser will show a local cached page. You'd rather cache pages on your server - you can even cache them indefinitely, if they don't have any dynamic parts - and if you edit the post or page, it will rebuild on the server. The browser should really not cache pages.
Static assets (images, javascript files, css files, etc) should be cached by browser for a week or a month or however you want. These really don't change often. But pages should not be cached by a browser.