In most jurisdictions the DST rules and timezone offset change rarely. In some jurisdictions, they change more frequently. Over the whole world, they change often (dozens of times per year).
Worldwide there are several each year IIRC. There are a lot of small regional timezones you have to account for - at least two Native reservations have their own timezones, each offset by 15 minutes from the timezone of their surrounding region I believe, or at least they did a decade ago when I worked with all this.
Also political changes often bring TZ changes, most obviously when larger countries split into smaller ones. But changing trade patterns can lead to TZ and DST changes, such as when Samoa skipped forward 24 hours, skipping Dec 30 2011 completely, putting them in the same timezone as Australia and New Zealand.
taejo|4 years ago
spiralx|4 years ago
Also political changes often bring TZ changes, most obviously when larger countries split into smaller ones. But changing trade patterns can lead to TZ and DST changes, such as when Samoa skipped forward 24 hours, skipping Dec 30 2011 completely, putting them in the same timezone as Australia and New Zealand.
https://www.theguardian.com/world/2011/dec/30/samoa-loses-da...
It also had July 4 1892 occur twice, due to originally having moved back 24 hours to align with the US.