Javany11,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
.red{
font-size: 28px;
color: #FF0000;
}
</style>
</head>
<body>
<div id="num">0</div>
<script>
var a = 0, n = 60;
function fn()
{
a = ++a % n;
num.innerHTML = a ;
if(!a) num.classList.toggle("red")
window.setTimeout(fn, 100) // 1000
}
fn()
</script>
</body>
</html>