Convert all elements with 12-hour time to 24-hour automatically (for WhatsApp Web, but could be adapted easily)

12to24.user.js

// ==UserScript==
// @name         WAWeb 24-hourifier
// @version      0.4
// @description  Convert all elements with 12-hour time to 24-hour automatically (for WhatsApp Web, but could be adapted easily)
// @author       Greenscreener
// @homepage     https://grsc.cz/
// @match        https://web.whatsapp.com/*
// @grant        none
// @downloadURL  https://gist.githubusercontent.com/Greenscreener/4422f5be36752bc720cbc7222fb73cdc/raw/12to24.user.js
// @updateURL    https://gist.githubusercontent.com/Greenscreener/4422f5be36752bc720cbc7222fb73cdc/raw/12to24.user.js
// ==/UserScript==

function conv12to24(str) {
	const re = /^(\d\d?):(\d\d) ([ap])m$/
	const hr = parseInt(str.match(re)[1])
	const mi = parseInt(str.match(re)[2])
	const add = str.match(re)[3] === "p"
	return ((hr+12*add)%24).toString().padStart(2,"0")+":"+mi.toString().padStart(2,"0")
}
setInterval(() => {
  [
    ...document.body.getElementsByTagName("span"),
    ...document.body.getElementsByTagName("div")
  ].filter(e => e.innerText.match(/^\d\d?:\d\d [ap]m$/))
    .forEach(e => e.innerText = conv12to24(e.innerText))
}, 500)

function lastseenconv12to24(str) {
	const timepart = str.substring(19)
	const convtime = conv12to24(timepart)
	return (" last seen today at " + convtime)
}

setInterval(() => {
  [
    ...document.body.getElementsByTagName("span"),
    ...document.body.getElementsByTagName("div")
  ].filter(e => e.innerText.match(/^last seen today at \d\d?:\d\d [ap]m$/))
    .forEach(e => e.innerText = lastseenconv12to24(e.innerText))
}, 500)