Autosave in Pages for Mac activates for the current document only after you first manually save a new document Untitled.pages to some arbitrary name (e.g. mydoc.pages). Then, autosave acts on changes you make to the document, and given that criterion, may autosave every 5 - 10 seconds for local Mac storage, and 5 - 15 seconds with a healthy network connection to iCloud Drive. Upon closing the current document, quitting Pages, and at some future timeframe, one reopens the document, autosave remains active on that document.
If one does not manually save a Pages document and quits the application, all content is lost and is non-recoverable because Pages cleans up its temporary files.
I recommend that anyone using Pages also has the macOS built-in feature Time Machine enabled so as to automatically back up their Mac on the hour while the Mac is powered as this prevents the loss of saved Pages documents and provides the means to recover Pages documents that are lost, or mysteriously damaged. Apple's iCloud is not a backup solution.
Once one has edited a Pages document a few times, there is a feature on its File menu that allows you to review prior versions of the document content, and retrieve that if necessary. This is known as Revert To > Browse All Versions…