This trick will help you to know when did Google indexed your page the last time, you will get to know the exact date and time. The trick is very simple and its related to the Google’s “Cache”, but before sharing the trick I would like you to know some basics.
Whenever Google crawls a web page it takes a snapshot of that page and cache it as a backup for future use. For example if the original page is not available user could see the google cached version for reference.
Finally the trick is, when Google displays the cached web page it shows a header at the top of the page, which serves as a reminder that this is not necessarily the most recent version of the page. It also highlights your query words on the page to make it easier for you to see why the page is relevant for the particular query. Along with all of these it also shows you the date and time of when the page was indexed. That’s it, looking at the header details you can easily get to know when a particular page was indexed by google.