More timezone features and customization for sending timestamps

The new timestamps feature is awesome, but I've already seen people not realize that the timestamp was localized to them (or not realize the timestamp was a dynamic thing at all) and incorrectly assume it's a different timezone. It would be nice to have a format option that includes the timezone abbreviations so that people realize it is actually in their local time. It would also be nice if instead of just a handful of presets, we could customize by using our own patterns.