When you have AMP pages in the Google AMP cache you should link directly to them from your Ads and other places in order to take advantage of the (almost) instant page delivery available.
How do you find them?
This is a regular web page, built to AMP standards
Query the AMP Project for the URL of the cached page
This is the direct URL for the cached AMP page. It will show in the address bar after you query the AMP project
If your AMP cached page is out of date just going to the cached page directly using the cached page's URL will force an update to the page. The updated page will show to the NEXT viewer of the page. Be patient because the new version of the cached page will not be available for 15 seconds. Be sure to cleare your browser cache before viewing the new page.