I think we should either keep the full list of time zones or specify a zone that everything must be converted to (obviously, UTC). The problem with keeping offsets is that it loses critical information about the zone represented, like how to handle daylight savings changes. The advantage of storing a zone is to be able to do reasonable calculations for that zone, for which a simple offset wouldn't work. If we are storing an offset, then we may as well store UTC to make filtering possible or easier.

I still think storing zones will be a problem. We already may need to update the zone list, which will continue to change.