Hi, I wouldn’t call this a bug, but a potential database inefficiency. I’m working on a TZ parser and using it to explore the timezone transitions as specified by the timezone database. I’m looking at the Atlantic/Canary transition on 1980 Sep 28 0:00s. At this time the timezone transitions from a permanent saving of 1:00 and abbreviation of WEST to a rule based savings specified by EU: 1980-09-27 23:59:59u = 1980-09-28 00:59:59 WEST // as specified by 0:00 1:00 WEST 1980-09-28 00:00:00u = 1980-09-28 01:00:00 WEST // as specified by 0:00 EU WE%sT I.e. there is no change in offset, savings, or abbreviation. And then an hour later EU specifies a savings and abbreviation change: 1980-09-28 00:59:59u = 1980-09-28 01:59:59 WEST 1980-09-28 01:00:00u = 1980-09-28 01:00:00 WET My observation is that this is a lot of transitions for one night. Would it not be better to delay the transition from "0:00 1:00 WEST” to "0:00 EU WE%sT” by one hour, and thus have only one transition instead of two? Here is a change that does so: diff --git a/europe b/europe index c64c41b..630c234 100644 --- a/europe +++ b/europe @@ -2922,7 +2922,7 @@ Zone Africa/Ceuta -0:21:16 - LMT 1901 Zone Atlantic/Canary -1:01:36 - LMT 1922 Mar # Las Palmas de Gran C. -1:00 - CANT 1946 Sep 30 1:00 # Canaries T 0:00 - WET 1980 Apr 6 0:00s - 0:00 1:00 WEST 1980 Sep 28 0:00s + 0:00 1:00 WEST 1980 Sep 28 1:00s 0:00 EU WE%sT # IATA SSIM (1996-09) says the Canaries switch at 2:00u, not 1:00u. # Ignore this for now, as the Canaries are part of the EU. Howard