This bookmarklet (I prefer to do it on purpose, not by default) would do this on a GitHub page. It is easy to convert it to a userscript.
javascript:(function () { document.querySelectorAll("relative-time").forEach(function (el) { var p = el.parentNode; var t = el.title; var s = document.createElement("span"); s.innerHTML = t; p.removeChild(el); p.appendChild(s); }); })();
javascript:(function () { document.querySelectorAll("relative-time").forEach(function (el) { var p = el.parentNode; var t = el.title; var s = document.createElement("span"); s.innerHTML = t; p.removeChild(el); p.appendChild(s); }); })();