Not against zones; I was hoping to shine a light on all the complexity around the TZDB, which is a mapping of zones to switchover times. Eg, $ zdump -v US/

Not against zones; I was hoping to shine a light on all the complexity around the TZDB, which is a mapping of zones to switchover times. Eg, $ zdump -v US/Eastern | grep 2020 US/Eastern Sun Mar 8 06:59:59 2020 UT = Sun Mar 8 01:59:59 2020 EST isdst=0 gmtoff=-18000 US/Eastern Sun Mar 8 07:00:00 2020 UT = Sun Mar 8 03:00:00 2020 EDT isdst=1 gmtoff=-14400 US/Eastern Sun Nov 1 05:59:59 2020 UT = Sun Nov 1 01:59:59 2020 EDT isdst=1 gmtoff=-14400 US/Eastern Sun Nov 1 06:00:00 2020 UT = Sun Nov 1 01:00:00 2020 EST isdst=0 gmtoff=-18000 If everyone simply picked a zone and stayed there, without the switching schedule above, you'd only need a mapping of zone to GMT offset and be done with it.