blackmesa.js

function setTimer(date) {
  function update() {
    const now = (new Date).getTime();
    const diffSeconds = Math.floor((date - now) / 1000);
    const elem = document.querySelector(".lambda-incident div p");
    elem.textContent = diffSeconds > 0 ? "" + diffSeconds : "That's it.";
    if (diffSeconds > 0) {
      setTimeout(update, 1000);
    }
  }
  update();
}

function makeDate(month, day, year, hour, minute, second) {
  return(new Date(month + " " + day + ", " + year + " " + hour + ":" + minute + ":" + second)).getTime();
}
const endDate = makeDate("September", 30, 2024, 23, 59, 59);
setTimer(endDate);