On Wed, 15 Jul 2026 at 16:27, Robert Bastian via tz <[email protected]> wrote:
> If TZDB continues to call them both EST, this will just shift the problem > to downstream users, because the real world will come up with distinct > names. > I very much doubt that having two definitions for each "xST" abbreviation within North America would be our preferred solution, both for cross-border reasons and legacy reasons related to GNU and RFC 822/5322. This is analogous to why we've preferred so far to use MST for British Columbia's UTC−7 and CST for Alberta's UTC−6, even though they might internally prefer PDT and MDT, respectively. Now, if this US bill becomes law, we'd be pretty squarely at the point where more folks in these North American zones are in "year-round daylight time" than not, and the weighing of concerns that went into those decisions could shift, as suddenly eastern Canada's *status quo* would likely be viewed as the exception on the continent. How zone names are used colloquially both internally and externally to each region would inevitably rebalance quite a bit… and I don't doubt the current cross-border political tension could complicate that. It may then make more sense to adopt year-round "xDT" nomenclature most places, and reserve "xST" for the areas retaining seasonal changes in the winter. (Of course, all the usual arguments against such nomenclature apply, but it might still be the "least bad" scenario for both intra- and international coordination — even if results in such "harmonized" designations changing in a few places where timekeeping hasn't, i.e., it could eventually become simpler to start thinking of Saskatchewan as MDT to match Alberta and Montana if both end up on year-round UTC−6.) Of course, within the US, the legal names of the zones would come along with this proposed shift and would happen automatically with the bill as-written. In Canada, timekeeping is a provincial/territorial matter, but there are federal zone names in the federal *Interpretation Act*, mainly to harmonize polling hours for federal elections — that likely will now need some updating anyway, but the optimal changes to minimize confusion might look different depending on whether the US moves ahead with its change. Meanwhile, it's also worth thinking about how this US proposal might affect border regions of Mexico: Mexico could straightforwardly enough choose to have Baja California rejoin Baja California Sur and Sonora on UTC−7, while border communities in western Chihuahua could rejoin the bulk of that state on UTC−6. I wonder, though, what would happen for border communities in eastern Chihuahua, Coahuila, Nuevo León, and Tamaulipas — adopting UTC−5 to match bordering Texas might be a bit awkward given the geography; then again, it's already the *status quo* for eight months of the year, so who's to say where that might ultimately land? -- Tim Parenti
