For most general workplace communications, the ASG recommends the 12 hour system because it is more familiar to more readers in Australia. For example, people are unlikely to misread a meeting time of ‘4 pm’, but some will be less familiar with the equivalent ‘16:00’.
However, you may find the 24 hour system efficient if your writing:
- is aimed at a specific audience where the 24 hour clock is more common, such as the emergency services or military
- involves detailed timetabling or scheduling, such as for online marketing campaigns.
Style basics
Use numerals followed by ‘am’ or ‘pm’, with a space in between
Use numerals for all times, followed by a space and a lower case ‘am’ or ‘pm’.
The abbreviation ‘am’ means ‘ante meridiem’ (before noon), while ‘pm’ is ‘post meridiem’ (after noon).
The minister will arrive at 11 am.
The minister will arrive at 11AM.
For midday and midnight, use 12 pm and 12 am respectively unless you think this might be confusing for your reader.
Hours and minutes
Use a full stop to separate hours from minutes
Where you need to give minutes, separate them from the hour with a full stop. Don’t use a colon or comma.
But only give the minutes if you need to. Avoid ‘00’ as it clutters the page without adding value.
Are you available to meet at 9.15 am tomorrow?
The deadline for submissions is 4:00 pm on Thursday.
Spans
Unless you’re using words, separate your times with an en dash but watch the spacing
In body text, particularly in formal writing, it’s best to avoid dashes in time spans.
In tables, graphics and other places with limited space:
- separate the numerals with an unspaced en dash for times from the same period of the day (such as both ‘am’)
- use a spaced en dash for times from different periods (such as ‘am’ then ‘pm’).
For times from the same period, you don’t need to repeat the ‘am’ or ‘pm’.
| Time period | Body text | Tables and graphics |
| Same | from 10 to 10.45 am
between 10 and 10.45 am | 10–10.45 am
|
| Different | from 8.30 am to 2 pm
between 8.30 am and 2 pm | 8.30 am – 2 pm
|
24 hour time
Where 24 hour time is essential, format your times with a colon
