See "real" commit date / time in github (hour/day)

If you're looking for a way to display the date/time permanently without hovering (e.g. for screenshots), the above Javascript-based solutions do not match the latest Github HTML (see comments). And they did not take into account the fact that the timestamps are auto-updated based on a timer ("X minutes ago" has to change every minute), so they will periodically reappear.

The following script seems to work on Github as of 2020-01-27:

(function() {
    var els = window.document.querySelectorAll("time-ago,relative-time");
    els.forEach(function(el) {
        el.innerHTML = "on " + el.getFormattedTitle(); // original timestamp
        el.disconnectedCallback(); // stop auto-updates
    });
})();

You can make this a bookmarklet by prefixing the code with javascript: as in the other JS-based solution.

And if you want to make this a permanent fix, you can save this as a TamperMonkey/Greasemonkey script, as follows:

// ==UserScript==
// @name         Github: always show absolute times
// @match        https://github.com/*
// ==/UserScript==

(function() {
    setTimeout(function() {
        var els = window.document.querySelectorAll("time-ago,relative-time");
        els.forEach(function(el) {
            el.innerHTML += ' <span class="text-small">(' + el.title + ')</span>'; // set original timestamp
            el.disconnectedCallback(); // stop auto-updates
        });
    }, 100); // YMMV, experiment with the timeout
})();

That's not very pretty but it seems to do the job.

I tried @odony's TamperMonkey/Greasemonkey script on Chrome but couldn't get it to work. detachCallback() wasn't recognized. So instead of detaching any callbacks, I simply replaced the <relative-time> node.

// ==UserScript==
// @name         Github: always show absolute times
// @match        https://github.com/*
// ==/UserScript==

(function() {
    document.querySelectorAll("relative-time").forEach(function(el) {
        var parent = el.parentNode;
        var timestamp = el.title;
        var span = document.createElement("span");
        span.innerHTML = timestamp;
        parent.removeChild(el);
        parent.appendChild(span);
    });
})();

Sorry I haven't tested this with other browser, but since this is basic javascript, it should just work. :)

With a user stylesheet plugin (I'm using stylebot in chrome)

time {
  font-size: 0;
}
time:after {
    content: attr(data-original-title);
    font-size: 14px;
}

Update 2021: a bookmarklet remains the only option on GitHub.
See for instance "Displaying Real Commit Times in GitHub" from Justin Noel

javascript:(function() {    
  var style = document.createElement('style');
  document.head.appendChild(style);
  var sheet = style.sheet;
  sheet.addRule('time-ago:before,relative-time:before', 'content: attr(title);display: block;font-size: 0.5rem;');  
})()

This contrasts with GitLab 14.1 (July 2021)

User setting to display absolute times

GitLab displays relative times (for example, 30 minutes ago) in a lot of places.

You can now change your user profile preferences to display absolute times instead, for example, ‘May 18, 2021, 3:57 PM’.

Absolute times respect your browser settings and format dates and times based on your preferred locales, for example, British English over US English.

This new display option gives more information at a glance for users that need it for workflows like correlating actions in GitLab to external systems.

See Documentation and Issue.

With gitlab 10 I used this to add the tooltip title to the element as standard text:

javascript:(function() { 
  var relativeTimeElements = window.document.querySelectorAll("time");
  relativeTimeElements.forEach(function(timeElement){
    timeElement.innerHTML = timeElement.innerHTML +" -- "+ timeElement.getAttribute('data-original-title');
  })
}());

Here is one for Gogs

javascript:(function() {
     var items = Array.from(document.querySelectorAll('span,relative-time'));  items.forEach(function(item) {    item.innerText = item.getAttribute('data-content');    item.style.backgroundColor = '#eee';    item.style.padding = '5px';    item.style.color = '#333';    item.style.fontWeight = 'bold';  });})()