nekada,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
<script>
window.addEventListener('DOMContentLoaded', function() {
//секунды
var sec=7;
//минуты
var min=0;
function refresh()
{
sec--;
if(sec==-01){sec=59; min=min-1;}
if(sec<=9){sec="0" + sec;}
time=(min<=9 ? "0" + min : min) + ":" + sec;
[].forEach.call( document.querySelectorAll('.timer'), function(el) {
el.innerHTML=time
});
(+sec||+min) && setTimeout(refresh, 1000);
}
refresh()
});
</script>
</head>
<body>
<span class="timer"></span>
<span class="timer"></span>
</body>
</html>