In Part I we looked at how to write dates clearly, this post follows on from that and deals with the correct formats for times.
The 24-hour clock
The first point to mention is that the 24-hour clock is much less common in English than in German, for example. It’s basically only used in timetables, in some computer applications and by the military. So it sounds strangely formal if you say in a normal conversation I’ll meet you at fifteen forty-five and it is absolutely wrong to use the 24-hour clock with the word o’clock:
The film starts at 19 o’clock !
The 12-hour clock
There are two formats for the 12-hour clock:
10am ten o’clock (in the morning)
8.15pm quarter past eight (in the evening)
Which do you use when? The format on the left is used for agendas and formal or neutral emails – arranging a time for a meeting for example. The format on the right is more common in spoken English and in ‘chattier’ emails e.g. My plane was delayed so I didn’t get home till quarter to eleven.
The numerals format
Let’s look closer at the numerals format on the left: 10am and 8.15pm.
The zeros are omitted when talking about the full hour: 10am rather than 10.00am. The minutes are most commonly separated from the hour using a full stop: 8.15pm; but some people use a colon: 8:15pm.
am stands for the Latin ante meridiem (before midday, i.e. the time between midnight and noon). pm stands for post meridiem (after midday, i.e. the time between noon and midnight).
In British English am and pm are written without full stops directly after the number without leaving a space – this avoids confusion with the word am (part of the verb to be). In the USA, exactly the opposite is the case with style guides recommending using full stops and leaving a space 8.15 p.m. or 8.15 P.M.
The words format
am and pm are never used with this format:
ten o’clock am, quarter past eight pm
If it’s not already clear from the context which time of day you’re talking about add in the morning / afternoon / evening.
Confusing for Germans: in the UK people often say half five. This means half past five not half past four!
And finally …
When arranging times for international telephone or video conferences be sure to specify the time zone.