You will need to install a user script manager extension to install this script.
Sometimes it's handy to see the full date and time without having to hover over each relative "ago" time on the page. This is especially useful when copying PMs and comments for archiving purposes.
This is a very simple script. It won't work on the main feed because of when this script runs. I've tested it on the following pages in Firefox with the Greasemonkey extension.
If you want to try it on other pages, you'll have to include the page URL in the script options.