a.js

// ==UserScript==
// @name        Robin Time Left Printer
// @description Violently Butchered Robin Assistant
// @namespace   com.github.cptasgard
// @include     https://www.reddit.com/robin/
// @include     https://www.reddit.com/robin
// @version     1.0
// @author      LeoVerto, Wiiplay123, Getnamo, CptAsgard
// @match        https://www.reddit.com/robin
// @grant       none
// ==/UserScript==

function sendMessage(msg) {
  $(".text-counter-input")[0].value = msg;
  $(".text-counter-input")[0].nextSibling.click();
}

function addMins(date, mins) {
  var newDateObj = new Date(date.getTime() + mins * 60000);
  return newDateObj;
}

function timeLeft() { // mostly from /u/Yantrio
  var remainingMessageArray = $(".robin-message--message:contains('approx')");

  if (remainingMessageArray.length == 0) {
    //This shouldn't happen
    return "Unknown";
  }

  var message = remainingMessageArray.text();
  var time = new Date(jQuery(
    ".robin--user-class--system:contains('approx') .robin-message--timestamp"
  ).attr("datetime"));
  try {
    var endTime = addMins(time, message.match(/\d+/)[0]);
    var fraction = Math.floor((endTime - new Date()) / 60 / 1000 * 10) / 10;
    var min = Math.floor(fraction);
    var sec = Math.round((fraction - min) * 60);
    return min + " m " + sec + " s";
  } catch (e) {
    return "Fail";
  }

  //grab the timestamp from the first post and then calc the difference using the estimate it gives you on boot
}

function checkCommand(message) {
    if( message.toLowerCase() == "!timeleft" ) {
      var tl = timeLeft();
      var message = ["/me Time left: T", tl[0] === '-' ? 'plus ' + tl.substr(1) : 'minus ' + tl, 'and counting.'].join(' ');
      sendMessage(message);
    }
}

var observer = new MutationObserver(function(mutations) {
  mutations.forEach(function(mutation) {
    var added = mutation.addedNodes[0];

    // Filters all new messages
    if ($(added).hasClass("robin-message")) {
      var msg = added;
      var msgText = $(msg).find(".robin-message--message").text();
      //console.log(msgText)

      checkCommand(msgText);
    }
  });
});

observer.observe($("#robinChatMessageList").get(0), {
  childList: true
});