I had some support tickets about dates not showing properly for customers based in the America/Merida timezone. Essentially America/Merida permanently changed to -0500 (CDT) on October 31, 2021, and it appears that the NSTimeZone does not respect this change, and reports times as -0600 (CST). Creating a little test tool with the following code: +(void) run { NSArray<NSString *> * args = [[NSProcessInfo processInfo] arguments]; if ([args count] > 1) { NSString *timezone = args[1]; NSLog(@"custom TZ: %@", timezone); NSTimeZone * tz = [NSTimeZone timeZoneWithName:timezone]; [NSTimeZone setDefaultTimeZone:tz]; } NSDate * now = [NSDate date]; NSLog(@"Testing Dates: (local timezone : %@)", [NSTimeZone localTimeZone]); NSLog(@" (default timezone: %@)", [NSTimeZone defaultTimeZone]); NSLog(@" (is DST : %@)", [[NSTimeZone defaultTimeZone] isDaylightSavingTimeForDate:now] ? @"YES" : @"NO"); NSLog(@" (current cal-tz : %@)", [[NSCalendar currentCalendar] timeZone]); NSLog(@" (current locale : %@)", [[NSLocale currentLocale] localeIdentifier]); NSLog(@"Now: %@", now); } And running with the America/Merida timezone passed in, I'm getting the following output: custom TZ: America/Merida Testing Dates: (local timezone : Local Time Zone (America/New_York (EDT) offset -14400 (Daylight))) (default timezone: America/Merida (CST) offset -21600) (is DST : NO) (current cal-tz : America/Merida (CST) offset -21600) (current locale : en_US) Now: Tue May 14 15:06:14 2024 Running the same code on Linux via the GNUStep implementation of Objective-C, I get the correct output with America/Merida showing up as CDT (ie (is DST : YES)). Are there any good ways to work around this?