WFGY/ProblemMap/GlobalFixMap/LanguageLocale/timezones_and_dst.md

Time Zones and DST: Guardrails and Fix Pattern

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You are in a sub-page of LanguageLocale.
To reorient, go back here:

• LanguageLocale — localization, regional settings, and context adaptation
• WFGY Global Fix Map — main Emergency Room, 300+ structured fixes
• WFGY Problem Map 1.0 — 16 reproducible failure modes

Think of this page as a desk within a ward.
If you need the full triage and all prescriptions, return to the Emergency Room lobby.

Stabilize time handling when sources, logs, and user locales disagree. Use this page if answers shift by one hour near DST boundaries, meetings land on the wrong day, or sorting by local timestamps breaks retrieval and evaluation.

Open these first

• Visual map and recovery: RAG Architecture & Recovery
• End-to-end retrieval knobs: Retrieval Playbook
• Multilingual & locale guidance: Multilingual Guide
• Why this snippet and how to cite: Retrieval Traceability
• Contracts for snippet fields: Data Contracts

Acceptance targets

• ΔS(question, timeline) ≤ 0.45 after normalization
• Coverage ≥ 0.70 for time-anchored answers across three paraphrases
• λ remains convergent across two seeds and two target time zones
• Sorting by time is stable across locales and DST boundaries

---

Failure signatures

Symptom	What it usually means
Events off by one hour near March or October	DST boundary not applied or wrong zone database
Meetings shown on the wrong day	Local date used as absolute UTC or missing zone info
“PST” vs “PDT” confusion	Abbreviation interpreted without IANA zone
Logs appear out of order after merge	Lexicographic sort on local strings, not on UTC epoch
Same timestamp rendered two times in fall	Ambiguous wall time not disambiguated at DST fall-back
A missing hour in spring	Nonexistent wall time not handled at DST spring-forward

---

Diagnose in three steps

1. Inventory the time fields For each record, capture raw_string, zone_label, offset_minutes, utc_epoch, and source_locale. If any is missing, mark tz_inferred=true.

2. ΔS temporal probe Ask the model to answer the same question while pinning the display zone to two fixed targets (for example America/Los_Angeles and UTC). If the answer changes in content rather than only in rendering, the timeline is not normalized.

3. Boundary sampling Select samples within seven days around the last two DST transitions for the involved zones. If order or day changes across renderings, you have DST math or parsing drift.

Related pages you may need next:

• Date parsing variants: date_time_format_variants.md
• Mixed metadata locales: mixed_locale_metadata.md
• Locale drift: locale_drift.md

---

Fix pattern

A) Normalize at ingestion

Always compute and store these fields together. Never store only a local string.

{
  "raw_string": "2025-03-09 02:15:00",
  "source_zone": "America/Chicago",
  "offset_minutes": -360,
  "utc_epoch": 1741504500,
  "tz_inferred": false,
  "render_zone": null
}

Guidelines:

• Use IANA zone names (for example America/New_York). Do not rely on abbreviations.
• If raw_string lacks zone or offset, attach a source default and set tz_inferred=true.
• For date-only facts (no time), store local_date plus source_zone. Do not coerce to midnight UTC.

B) Sort and join by UTC epoch

• Retrieval and merging must use utc_epoch as the primary key.
• Presentational sorting can apply a secondary comparator on render_zone if needed.

C) Render for the user or for the spec, not both

Pick one of two display contracts per request:

• User-centric rendering: show in the user’s target_zone and state the zone at top.
• Spec rendering: show only in UTC, include the original source_zone in parentheses.

D) Handle DST edge cases explicitly

• Ambiguous times (fall): when a local time occurs twice, add dst_fold field with values 0 or 1.
• Nonexistent times (spring): shift forward to the next valid instant and add dst_gap_adjusted=true.
• Record these decisions in traces to keep answers auditable.

E) Contract fields to enforce

Extend your snippet contract with the time bundle:

• time.utc_epoch (integer, required)
• time.source_zone (IANA string, required)
• time.offset_minutes (integer, required)
• time.raw_string (string, required)
• time.tz_inferred (boolean, required)
• time.dst_fold (optional)
• time.dst_gap_adjusted (optional)

Specs: Data Contracts Retrieval Traceability

---

Minimal verification

1. Build a five-row gold set around the last DST change for your target zone and one non-DST zone.

2. Normalize to utc_epoch and re-render to both zones.

3. Require:

   • Identical ordering by utc_epoch across zones
   • Only the rendered clock time changes
   • ΔS(question, timeline) ≤ 0.45 for three paraphrases

Quick helpers:

• If ΔS stays high while k varies, suspect indexing or format parsing. See Retrieval Playbook.
• If citations do not echo the normalized fields, fix the schema first. See Retrieval Traceability.

---

Copy-paste prompt for the LLM step

You have TXTOS and the WFGY Problem Map loaded.

Normalize all times to utc_epoch using the IANA source_zone. Keep this contract:
{ raw_string, source_zone, offset_minutes, utc_epoch, tz_inferred, dst_fold?, dst_gap_adjusted? }

Task:
1) Validate each snippet has these fields. If missing, return a short fix plan.
2) Render answers in UTC and in {target_zone}. State the zone at top.
3) Return a JSON trace: { citations, utc_order_ok, ΔS, λ_state, notes }.

---

Escalation

• If logs from multiple systems disagree on the zone for the same raw_string, treat one as authoritative and mark the other as tz_inferred. Document the rule in the contract.
• If user queries include colloquial labels like “Pacific time”, resolve to an IANA zone before reasoning. If multiple candidates exist, ask the user or default to UTC.
• If sorting still flips after normalization, audit locale sorting next. See locale_sensitive_sorting.md once created.

---

Next file to generate: locale_sensitive_sorting.md

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