This is improved @Vicky solution - it has clearInterval() added so it prevents a loop of reloading if the redirect takes too long:
$(document).ready(function () {
var myTimer = window.setInterval(function () {
var timeLeft = $("#countdown").html();
if (eval(timeLeft) == 0) {
console.log('Now redirecting');
clearInterval(myTimer);
window.location = ("@Html.Raw(HttpUtility.HtmlDecode(redirectUrl))");
} else {
$("#countdown").html(eval(timeLeft) - eval(1));
}
}, 1000);
});