Note that strftime does not produce unambiguous time zone names. The four-letter Australian time zones are printed with names such as EST and CST. Better use -0500, +0545 and the likes, as suggested by ISO 8601.
If you want to indicate a time zone you shouldn't just use the offsets - they're ambiguous in that several different time zones can have the same offset at any point in time.
Better (IMO) to use the zoneinfo ID, e.g. "Europe/London" - along with the offset as well, in case the local time is ambiguous in that time zone due to a daylight saving transition.
