https://niko.institute/js/countdown.js?v4

1(function () {
2    const second = 1000,
3        minute = second * 60,
4        hour = minute * 60,
5        day = hour * 24;
6
7    const x = setInterval(function () {
8
9        const now = new Date().getTime();
10        const distance = (eventStartTime * 1000) - now;
11
12        document.getElementById("countdown-days").innerText = Math.floor(distance / (day));
13        document.getElementById("countdown-hours").innerText = Math.floor((distance % (day)) / (hour));
14        document.getElementById("countdown-minutes").innerText = Math.floor((distance % (hour)) / (minute));
15        document.getElementById("countdown-seconds").innerText = Math.floor((distance % (minute)) / second);
16
17        if (eventStartTime * 1000 <= now && eventFinishTime * 1000 + day >= now) {
18            document.getElementById("countdown-text").innerText = "Внимание!";
19            document.getElementById("countdown").style.display = "none";
20            document.getElementById("countdown-content").style.display = "block";
21            clearInterval(x);
22        } else if (eventFinishTime * 1000 < now) {
23            document.getElementById("countdown-text").innerText = "Внимание!";
24            document.getElementById("countdown").style.display = "none";
25            document.getElementById("countdown-content-finish").style.display = "block";
26            clearInterval(x);
27        }
28    }, 0)
29}());