How can I make a jQuery countdown

I thought I would break this up a bit and provide something that does both countdown, and redirection. After all, you may want to countdown and manipulate the DOM instead tomorrow. As such, I’ve come up with the following jQuery plugin that you can use, and study:

// Our countdown plugin takes a callback, a duration, and an optional message
$.fn.countdown = function (callback, duration, message) {
    // If no message is provided, we use an empty string
    message = message || "";
    // Get reference to container, and set initial content
    var container = $(this[0]).html(duration + message);
    // Get reference to the interval doing the countdown
    var countdown = setInterval(function () {
        // If seconds remain
        if (--duration) {
            // Update our container's message
            container.html(duration + message);
        // Otherwise
        } else {
            // Clear the countdown interval
            clearInterval(countdown);
            // And fire the callback passing our container as `this`
            callback.call(container);   
        }
    // Run interval every 1000ms (1 second)
    }, 1000);

};

// Use p.countdown as container, pass redirect, duration, and optional message
$(".countdown").countdown(redirect, 5, "s remaining");

// Function to be called after 5 seconds
function redirect () {
    this.html("Done counting, redirecting.");
    window.location = "http://msdn.microsoft.com";
}