The load time saved on each cached page varies depending on the amount of content on the page. Your internal clock may be able to notice the difference in page load times, but why not have your browser do it? Each browser has tools that allow you to view various page elements. In the Google Chrome's Developer Tool, for example, select the Timeline tab) to check the page load time.
In a browser tab, signed in as the page author, clear the page cache. In a private or incognito browser tab, not signed in and with the browser timeline visible, reload the page to see the cached response time.