TL;DR: Military HHMM local repeats twice yearly adjustment—spring skip hour, fall repeat hour. UTC/Zulu unaffected; annotate “DST active” on spring/fall week schedules.
Spring forward gap
2:00 AM → 3:00 AM local means 0230 may not exist that night—schedulers avoid critical events in gap window.
Fall back ambiguity
1:00 AM occurs twice—log which occurrence with UTC offset or sequential event ID.
UTC stable reference
1500Z same worldwide regardless US DST—pilots plan fuel on Zulu.
Shift workers paid hour
Payroll laws vary on repeated hour—HR policy not clock arithmetic blog scope but ops must know paycheck impact.
Automated scheduler bugs
Cron jobs firing local 0230 die spring week—migrate critical jobs to UTC cron.
Calendar invites
Outlook “adjust for daylight saving” checkbox—verify March invite still 1400 after transition Sunday.
International colleagues
Arizona no DST; EU different switch dates—world clock row per contact for two weeks surrounding March/April.
Documentation banner
Email footer first week DST “all times local EDT”—remove banner after team adapts.
Practice conversion
Convert usual 0700 standup across DST boundary using converter plus calendar offset note in runbook.
Historical incident review
Mis-timed backup job classic DST postmortem—add UTC logging permanently after once.
Cron UTC migration
Critical jobs on UTC cron survive spring gap local 0230 missing hour.
Payroll repeated hour policy
Fall back 1 AM twice—HR defines pay rule; ops documents clock display.
Arizona no DST peer row
World clock Arizona plus EU different switch dates—two-week alert banner.
Email footer DST week
All times local EDT—remove banner after team adapts.
Historical backup job postmortem
One DST miss → permanent UTC logging adoption story.
0230 that does not exist on the spring-forward night
On the spring-forward night, local clocks jump from 02:00 to 03:00. A stamp of 0230 local does not exist. A backup job, a medication, or a bus that says 0230 that night needs a new plan before the night arrives. Move it to 0115 or to 0315, and write the choice down. Leaving 0230 and hoping the software will “do something sensible” produces a skip or a double, and you will not know which until the thing fails.
The same instant still exists in UTC. If the job can run on UTC, schedule it in UTC and it will not fall into the hole. If the job is a local bus, UTC does not drive the bus. The bus needs a new local stamp. Do not give the bus a UTC answer. Match the fix to the thing that has to happen in local morning.
Fall-back hour that happens twice
On the fall-back night, 0130 local happens twice. A log that says 0130 is ambiguous. Disambiguate with the offset, or with a note “first 0130” and “second 0130,” or by writing UTC. A medication schedule that says 0130 on that night is not specific enough to administer. Choose the first or the second in advance, in writing, while you are awake in the daytime. The night is a bad time to invent the rule.
Payroll for a shift that works the repeated hour must say whether that hour is paid once or twice. The clock will not tell you. The policy will. A policy sentence: “the repeated hour is paid.” Or the opposite. Silence becomes a grievance. The stamp 0130 is not the grievance. The missing sentence is.
Arizona colleague who does not share the hole
A colleague in a place that does not observe the shift, such as most of Arizona, does not have a missing 0230. Your 0315, after the jump, may be their 0315 or not, depending on the rest of the offset. Do not say “I moved it an hour, you move yours.” Send the UTC instant or a full offset stamp. “03:15 with offset −04:00 after the jump” is a sentence they can convert. “I moved the job” is a riddle.
Banner week on the calendar invite
For the week of the change, the invite’s first line should name the condition. “After spring jump: 0315 local, 0230 does not exist.” Remove the banner the following week. A permanent banner becomes wallpaper. A missing banner on the danger week is how someone schedules 0230 again because last year’s invite was copied. Copy the agenda. Do not copy the stamp without reading the banner line. The banner is the part that expires, and the expiry is a feature.
Bus placard that says 0315 after the jump
The bus that used to leave at 0230 needs a placard the afternoon before the jump. The placard says “this Sunday 0315, the 0230 trip does not run.” It does not say “one hour later” without a stamp. Riders do arithmetic wrong when they are cold. 0315 is a stamp they can compare to a phone. Take the placard down on Monday. A placard that stays up will cancel a real 0230 in June, when 0230 exists again.
Tell the driver the same stamp the placard uses. A driver who was briefed “leave an hour later” may leave at 0330 if they start from 0230 and add an hour, or at 0315 if they start from 0215. Say 0315. Put it on their run sheet. The placard and the run sheet must match, or the rider and the driver will do different math and both will feel cheated.