1. Scope
Finds working-hour overlap between two or more teams in different time zones and surfaces daylight-saving-time pivots. Not a scheduling engine — output is informational.
2. Inputs and outputs
Inputs
- timezones array
Each: IANA zone, working-hours window.
Outputs
- overlapWindows
UTC ranges with overlap across all members.
- dstWarnings
Dates where DST changes shift the overlap window.
Engine source: src/lib/time-zone-overlap-planner/engine.ts
3. Formula / scoring logic
for each UTC hour h in [0..23]:
if h is inside every member's local working hours → overlap
4. Assumptions
- Working hours are entered in local time per member.
- Uses IANA time zone database via the browser's Intl API — subject to the browser's bundled TZDB version.
5. Data sources
- IANA Time Zone Database as of 2024b
6. Known limitations
- Cross-hemisphere DST offsets (e.g. US fall-back vs EU fall-back 1 week apart) can temporarily narrow or widen the overlap — the tool surfaces the warning but does not auto-reschedule.
7. Reproducibility
Input
members = [Berlin 9–17, NYC 9–17].
Expected output
overlap ≈ 15:00–17:00 Berlin / 09:00–11:00 NYC (standard time); DST warning active for the two weeks each spring/fall when offsets diverge.
8. Change log
- 2026-04-24 methodology page first published.
Worked example
Run live against the same engine this site ships
(/engines/time-zone-overlap-planner.js).
The inputs and outputs below are recomputed on every build and
independently re-verified in CI — they are never hand-authored.
Input
- tool
- timezone_overlap_planner
- meeting_duration_minutes
- 60
- start_date
- 2026-03-10
- range_days
- 7
- slot_interval_minutes
- 30
- participants[0].id
- nyc
- participants[0].name
- New York
- participants[0].time_zone
- America/New_York
- participants[0].work_start_hour
- 9
- participants[0].work_end_hour
- 17
- participants[1].id
- lon
- participants[1].name
- London
- participants[1].time_zone
- Europe/London
- participants[1].work_start_hour
- 9
- participants[1].work_end_hour
- 17
- participants[2].id
- blr
- participants[2].name
- Bangalore
- participants[2].time_zone
- Asia/Kolkata
- participants[2].work_start_hour
- 10
- participants[2].work_end_hour
- 19
Output
- warnings[0]
- No overlap windows found under current working-hour constraints.
- assumptionsEcho.participantCount
- 3
- assumptionsEcho.meetingDurationMinutes
- 60
- assumptionsEcho.startDate
- 2026-03-10
- assumptionsEcho.rangeDays
- 7
- assumptionsEcho.slotIntervalMinutes
- 30
Frequently asked questions
- What does the Time Zone Overlap Planner calculate?
- Finds working-hour overlap between two or more teams in different time zones and surfaces daylight-saving-time pivots. Not a scheduling engine — output is informational.
- What inputs does the Time Zone Overlap Planner need?
- It takes 1 input: timezones. Outputs returned: overlapWindows, dstWarnings.
- What formula does the Time Zone Overlap Planner use?
- The exact computation is: for each UTC hour h in [0..23]:; if h is inside every member's local working hours → overlap;
- Can I verify the Time Zone Overlap Planner with a worked example?
- Yes. With members = [Berlin 9–17, NYC 9–17]. the tool returns overlap ≈ 15:00–17:00 Berlin / 09:00–11:00 NYC (standard time); DST warning active for the two weeks each spring/fall when offsets diverge.
- Where does the Time Zone Overlap Planner get its benchmark data?
- Reference data is sourced from: IANA Time Zone Database (as of 2024b).
- What can the Time Zone Overlap Planner not tell me?
- Known limitations: Cross-hemisphere DST offsets (e.g. US fall-back vs EU fall-back 1 week apart) can temporarily narrow or widen the overlap — the tool surfaces the warning but does not auto-reschedule.