var timer2 = "5:01";
var interval = setInterval(function() {
var timer = timer2.split(':');
//by parsing integer, I avoid all extra string processing
var minutes = parseInt(timer[0], 10);
var seconds = parseInt(timer[1], 10);
--seconds;
minutes = (seconds < 0) ? --minutes : minutes;
if (minutes < 0) clearInterval(interval);
seconds = (seconds < 0) ? 59 : seconds;
seconds = (seconds < 10) ? '0' + seconds : seconds;
//minutes = (minutes < 10) ? minutes : minutes;
$('.countdown').html(minutes + ':' + seconds);
timer2 = minutes + ':' + seconds;
}, 1000);