This pretty much breaks progressive enhancement. If anything, the user's time zone should be first estimated from their IP address with a setting to override it. The client side solution to further refine it should be piled on top of this last, if possible. JavaScript is useful, but nobody should assume it's present.
Also, it should be noted which time zone a time is in. A naked date/time is about as useful as saying that you're 3 units away from me. What unit does "unit" represent? shrug
Also, it should be noted which time zone a time is in. A naked date/time is about as useful as saying that you're 3 units away from me. What unit does "unit" represent? shrug