I have a task to show digital clock (with minutes precision) on HTML page in some fixed timezone (MSK or MSD - depending on current date). I'd like to avoid relying on client system clock, so some synchronization with server is required. HTTP server sends Date header in each response so we can send an AJAX GET or HEAD request to any URL of our site to get server date, calculate the difference with client date and use it when updating clock with setTimeout().
There are other issues remains: timezone switching for daylight settings, latency accounting for very slow connections.

Any idea to this task the simpliest way? I'd prefer to solve it without server-side programming.