A crude (but working) tampermonkey/violentmonkey script to change most 12h time displays into 24h format in Google Maps (since they cant be bothered to add "English (UK)" language option...). This will probably break if they ever change the jslog ids or the general layout of the page.

google_maps_24h_time.user.js

// ==UserScript==
// @name         Google Maps 24h Time Converter
// @namespace    http://tampermonkey.net/
// @version      1.0
// @description  Convert most am/pm times to 24-hour format on Google Maps
// @author       You
// @match        https://www.google.com/maps/*
// @grant        none
// ==/UserScript==

function convertAmPmTo24h(text) {
  const ampmRegex = /\b(\d{1,2})(?::(\d{2}))?\s*(am|pm)\b/gi;

  return text.replace(ampmRegex, (_, hour, minute, meridiem) => {
    hour = parseInt(hour, 10);
    minute = minute ? parseInt(minute, 10) : 0;

    if (meridiem.toLowerCase() === 'pm' && hour !== 12) {
      hour += 12;
    } else if (meridiem.toLowerCase() === 'am' && hour === 12) {
      hour = 0;
    }

    const hh = hour;
    const mm = minute.toString().padStart(2, '0');

    return `${hh}:${mm}`;
  });
}


(function() {
    'use strict';

    function replace_preview(){
      // previews on businesses without multiple hour categories (without a full view after click)
      document.querySelectorAll('[jslog^="14925"] span:not(:has(*))').forEach(span => {
        span.innerText = convertAmPmTo24h(span.innerText)
      })

      // for the above but user expanded the preview inline
      document.querySelectorAll('[jslog^="36914"] li:not(:has(*))').forEach(li => {
        li.innerText = convertAmPmTo24h(li.innerText)
      })

      // previews on businesses with one "hours"
      document.querySelectorAll('[jslog^="36914"] span:not(:has(*))').forEach(span => {
        span.innerText = convertAmPmTo24h(span.innerText)
      })

    }

    function replace_full_view(){
      document.querySelectorAll('h1.fontTitleLarge').forEach(h1 => {
        h1.parentElement.parentElement.parentElement.parentElement.parentElement.querySelectorAll('div[role=main] > div:nth-child(2) table li').forEach(li => {
          li.innerText = convertAmPmTo24h(li.innerText)
        })
      })
    }


    function replace_carousel() {
      document.querySelectorAll('[jslog="24224"] span:not(:has(*))').forEach(span => {
        span.innerText = convertAmPmTo24h(span.innerText)
      })
    }

    function tick(){
      replace_preview();
      replace_full_view();
      replace_carousel();
    }
    
    setInterval(tick, 25)
    tick()
})();

Is there a way to get the textbox working as well to display 24-hour format?

Is there a way to get the textbox working as well to display 24-hour format?

I think that may require reimplementing the whole textbox or adding some sort of wrapper around it, but if you find a way and want to add your contribution feel free to post your version of the script here