24-hour Time Format
ISO date-and-time representation uses a 24-hour clock for standardized interchange. A form such as 18:00 avoids the a.m./p.m. distinction, but punctuation, seconds, time-zone information, and human-facing presentation still depend on the applicable standard or house style.
In standardized 24-hour time, hours run from 00 through 23; write the time in the format required by your standard or house style, such as 18:00 when minutes are shown.
Key details
Important caveats
Usage Boundary
Do not assume that every human-facing publication must use ISO punctuation or precision; follow the required operational standard or editorial style.
Further guidance
Standard Basis
ISO date/time conventions use a 24-hour clock for standardized representations.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- ISO 8601 — Date and time format (opens in a new tab)International Organization for Standardization · ISO overview of unambiguous date/time representation including YYYY-MM-DD