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Dates should usually be spelled out in full:
24 October 2007
The month is capitalised and there are no commas separating the elements.
If you say what day it fell on, then there are still no commas:
Wednesday 24 October 2007
If there are a lot of dates, as in a table, use the abbreviated form, with slashes dividing the elements:
24/10/07 or 24/10/2007
For times, use the twelve-hour clock and separate the minutes from the hours with a colon:
1am, 3:30pm, 6.15am, 9.07pm
The British convention was always to use a point between the hour and the minute, but because of computers the colon has become so widespread that insisting on a point would cause too much confusion.
Don’t put points in ‘am’ and ‘pm’ – it looks too fussy.
In case you’re interested, ‘am’ stands for ‘ante meridiem’, meaning ‘before midday’, while ‘pm’ stands for ‘post meridiem’ or ‘after midday’. This causes confusion over whether midday itself should be 12am or 12pm, since it’s neither before nor after midday. The best way to handle this is to use the words ‘midnight’ or ‘midday’ (or ‘noon’ if you prefer, and are consistent), so that there’s no possible confusion. If you are forced to take a position, it’s best to use 12am for midnight and 12pm for midday.
In narrative text (books or articles), if there aren’t too many times to deal with, it’s more friendly to spell them out as they’d be spoken:
four o’clock, quarter to three, half-past seven, etc.