It is said that the 'early bird catches the worm'. A rooster will crow 'cock-a-doodle-doo' at dawn. Maybe you get up at the crack of dawn or fall asleep at dusk. But what time is it exactly? Is it 8am or 8 o'clock? Do I read 8:15 as quarter past or 15 minutes after 8?
When it comes to reading and writing the time, 'a.m.' is reserved for the
morning hours, before 12pm. After midday, 'p.m.' indicates the 12 hours until
midnight.
'O'clock' is only ever used for precise hours. If it’s 'eight-oh-one' (8:01),
you can’t use 'o’clock'! So 1, 2, 3…, 11 and 12 o'clock are the only 12
o'clocks you’ll get! 13:00 is never 13 o'clock, but 1 o'clock or '1pm'.
We will talk of 'minutes past an hour' only for 30 minutes past an hour. At
6:31, we start looking forward. It is closer to the next hour: 6:31 is 'twenty
nine minutes to seven'! We only have a 'half past, never a ‘half to'.
'Quarter past' and 'quarter to' are reserved for X:15 and X:45. The preposition
'at' usually indicates time: 'Stop by at 8' or 'The show starts at nine forty
five' (or quarter to ten or 9:45).
Phrases like 'in the morning', 'in the evening', 'past the hour' and 'minutes
to the hour' are very common: 'It’s eight in the morning'; 'The guests will
arrive at 6 in the evening' (6pm or 18:00); 'It's ten past five (17:10). We
need to get ready'; 'Its 5 minutes to 6! The guest will be here soon! (17:55)';
'It’s six fifteen (or quarter past six or 18:15). The guests are arriving'.
18:15 can be said as 'six fifteen' or 'quarter past six'
18:45 can be 'quarter to seven' or 'six forty five', but is never 'forty five
minutes past six'!
08:00 is 'eight o'clock', eight A. M.' or 'eight in the morning'
12:00 is 'midday', 'noon’, 'twelve P M' or 'twelve o'clock'
00:00 is 'midnight'
So the next time you get up at the crack of dawn, you'll know that it's six am,
six o'clock or six in the morning!