the above tl;dr forgot something massive: all current protocols are unsafe (e.g. need exporting the entirety of org.kde.* in dbus) and/or only work on X11
ISO 8601 contains way too many obscure formats. RFC 3339 is pretty much a subset and defines only sensible ones. It also allows 2018-02-05 08:02:43-00:00 (no T and explicitly specifying no timezone)
atbge