Time zone research
Time Zones That Are Not on the Hour
Three zones in the selected ten-zone 2026 evidence set use offsets that are not a whole number of hours. Kolkata and Kathmandu stay on fractional offsets throughout the sampled year, while Chatham moves between two forty-five-minute offsets. Those measured cases show exactly why whole-hour arithmetic is insufficient for the zones represented here.
What this guide helps you decide
If I assume every time zone is a whole number of hours from UTC, what breaks?
This research reports offsets read from the runtime's own time-zone database for 2026. It does not claim a complete list of non-hour offsets and does not describe the history or politics of any zone.
Try it on the anchor product: BeanNest Time /, BeanNest Time /converter/.
The measured fractional offsets
Asia/Kolkata is +05:30 in January and July with zero recorded transitions. Asia/Kathmandu is +05:45 in both samples with zero transitions. Pacific/Chatham is +13:45 in January and +12:45 in July and has two recorded 60-minute transitions during 2026.
Whole-hour arithmetic loses thirty or forty-five minutes
For the measured Kolkata and Kathmandu cases, replacing the recorded offset with a whole-hour value necessarily discards 30 or 45 minutes. The error comes from the representation itself, so repeating the same whole-hour shortcut repeats the same displacement.
Chatham combines a fractional base with offset changes
Chatham demonstrates that fractional offset and seasonal offset change are separate properties. Both of its measured 2026 offsets end in :45, while the transition delta is one hour. Handling only whole-hour zones or only constant fractional zones would miss that combination.
Three of ten describes this evidence set only
The generator reports nonHourOffsetZoneCount as 3 for a ten-zone set chosen to cover distinct scheduling cases. That count is not a population estimate for the world's time zones and should not be converted into a claim about how common fractional offsets are globally.
Verify the exact zone and date
A reliable conversion resolves the offset for the specific zone identifier and instant from a time-zone database. The evidence generator follows that approach, which is why the same file can represent both constant fractional offsets and Chatham's two 2026 states without a hand-maintained shortcut.
The evidence does not explain why a jurisdiction chose an offset
This corpus records offset values and transitions, not political history, solar-time history, legislation, or administrative reasoning. Those topics require different sources. The guide therefore limits its conclusion to the measured arithmetic and scheduling consequences of the offsets in the evidence file.
First-party evidence and provenance
How we checked this
We derived every offset and transition from the runtime's own time-zone database by sampling the zone offset hourly across the calendar year, then modelled a weekly meeting pinned to a fixed local wall-clock time in a reference zone. The generator is in this repository and the evidence file is its output. For this guide we read the January and July offset for each zone in the set and identified those whose offset is not a whole number of hours, including one that changes between two such offsets.
- Method
- We derived every offset and transition from the runtime's own time-zone database by sampling the zone offset hourly across the calendar year, then modelled a weekly meeting pinned to a fixed local wall-clock time in a reference zone. The generator is in this repository and the evidence file is its output.
- Environment
- Node.js on a desktop workstation, using the bundled IANA time-zone data. No network call, no hard-coded offset table, and no user data.
- Captured
- Reviewed by
- BeanNest Studio
Repository evidence artifacts:
tools/research-evidence/time/transitions-2026.jsontools/research-evidence/time/README.md