override Deferred.loop(fork from JSDeferred Sample's aloop;)). Timer is gist:50500.

gistfile1.js

Deferred.loop = function(n, f) {
	var i = 0;
	var end = new Object;
	var ret = null;

	return Deferred.next(function() {
		var t = new Timer;
		t.start();

		try {
			do {
				ret = f(i);
				if (++i >= n) throw end;
			}
			while (t.count() < 50);
			return Deferred.call(arguments.callee);
		}
		catch(e) {
			if (e == end) return ret;
			else throw e;
		}
	});
};
Deferred.register('loop', Deferred.loop);