if-modified-since-header

This plugin is made with a piece of code given by an author named Cybmeta to Saumya Majumder as you can verify here : https://wordpress.stackexchange.com/questions/172966/if-modified-since-http-header 2nd issue : it doesn’t work in a proper manner, the date/time format is wrong, the result is always 200 ok even if the page haven’t change (correct answer is 304 not modified in this case).

Installed. Went to https://varvy.com/tools/if-modified/ does not work. Uninstalled.