That’s what it does… but in most cases, guests don’t need a true “live” view.
By setting it to 30 seconds, if you did not have tons of users in the site, that cached page would never get re-used. You spent a bunch of server resources writing that page to disk that never got used because no one was really accessing it within the next 30 seconds.
Think of it this way… Google bot comes to your site. It starts on the homepage. That’s now told your server to not just deliver that page to Google but make a version of it for offline use and to hold onto it for 30 seconds. The rest of the time, Googlebot was not on your homepage. They were on the inside content of your pages. Triggering the same thing all over again creating a cached version that no one else ever accessed in the next 30 seconds.
Is there some value gained by a guests like Google seeing data “real time”? Having content delayed a few minutes won’t make a huge difference for them.
However if you honestly did feel it was critical… Instead of trying to cache at the server level that low, the page experience would be faster by not caching that base page at all.
With a CDN, you also have the fact that each CDN POP is unique. Cloudflare has over 300 locations. This means if you have someone accessing content in LA, its cache timer is separate from the servers in Miami. (Each has its own timer based on how long it’s been since that specific server last accessed it.)
Super short cache periods for base pages only help if you’re operating a hugely busy site like CNN, Wikipedia, etc.
Also remember a CDN has an extra benefit over server caching… the CDN can cache most all objects. This means images, style sheets, JS, etc all can be cached for DAYS whereas the base HTML page might be cached for a few minutes. This can reduce origin bandwidth by 50-90 percent depending on how dynamic the base pages are.