discord-proper-time.js

(function() {
	// see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleString
	// default en-GB will give you DD/MM/YYYY hh:mm::ss
	let dateLocales = "en-GB";
	let dateOptions = undefined;
	// (making it easier to restart by pasting the edited snippet)
	if (window.properTimes) {
		clearInterval(window.properTimes);
		for (let el of document.querySelectorAll(`time:not(.proper-time)`)) {
			el.classList.remove(`proper-time`);
		}
	}
	window.properTimes = setInterval(function() {
		let today = new Date().toLocaleDateString(dateLocales, dateOptions);
		for (let el of document.querySelectorAll(`time:not(.proper-time)`)) {
			el.classList.add(`proper-time`);
			let dt_str = el.getAttribute(`datetime`);
			if (!dt_str) continue; // (malformed? not really a timestamp? skip it)
			let dt = new Date(parseFloat(dt_str));
			let date = dt.toLocaleDateString(dateLocales, dateOptions);
			let time = dt.toLocaleTimeString(dateLocales, dateOptions);
			// use time if the message is from today, otherwise use date & time
			el.innerText = date == today ? time : date + " " + time;
		}
	}, 3000); // <- update interval, in milliseconds
})();