If you want to do timings from the client, then you'd have to use client-side programming; PHP runs on the server, so it's not going to help you. (Perhaps use Javascript and whatever it's http request object is called to request a page, and time how long that takes. I haven't done it, and I haven't seen it done, but that's more because I haven't had any reason to do it nor have I looked, not because I expect it would be all that difficult.)
