Paul.Koning@dell.com wrote:
As I recall, IETF made that point rather explicitly some time ago, after the Turkey and/or Egypt DST debacle.
Yes, the main tzdb page <https://www.iana.org/time-zones/repository/tz-link.html> now says, "If your government plans to change its time zone boundaries or daylight saving rules, let the mailing list know well in advance. With less than a year's notice there is a good chance that some computer-based clocks will operate incorrectly after the change, due to delays in propagating updates to software and data. The shorter the notice, the more likely clock problems will arise." It goes on to cite Matt Johnson's more-detailed blog post "On the Timing of Time Zone Changes" <http://codeofmatt.com/2016/04/23/on-the-timing-of-time-zone-changes/>. Perhaps the above info could be sent on the Tongan government, to give them an idea of the problems they'll face if they delay their decision further.