Try to remember the lists of the time words that need 'on', 'in', 'at' and some that don't need any prépositions at all.
But before try to remember that in general, we use:
|PRECISE TIME||MONTHS, YEARS, CENTURIES, SEASONS, LONG PERIODS||DAYS and DATES|
|At 5 o'clock.||In May.||On Sunday.|
|At 9.30 am.||In Summer.||On Tuesdays.|
|At noon.||In the Summer.||On March 6th.|
|At lunchtime.||In 1990.||On 25th Dec. 2015.|
|At bedtime.||In the 1990s.||On Christmas day.|
|At sunrise.||In the next century.||On Bastille Day.|
|At sunset.||In the Middle Ages.||On my birthday.|
|At the moment.||In the past / future.||On New Year's Eve.|
|At night.||The stars shine at night.|
|At the weekend.||I usually go to the cinema at the weekend.|
|At Easter / Christmas.||We usually stay with my family at Christmas.|
|At the same time.||They finished the race at exactly the same time.|
|At present.||He's not available at present.|
Notice the use of the preposition of time IN and ON in the following standard expressions:
|In the morning.||On Tuesday morning.|
|In the mornings.||On Sunday mornings.|
|In the afternoon(s).||On Monday afternoons.|
|In the evening(s).||On Wednesday evening.|
VERY IMPORTANT: When we say LAST, NEXT, EVERY, THIS we do not also use at, in, on.
I went to London last June. (
in last June)
He's coming back next Tuesday. (
on next Tuesday)
I go home every Easter. (
at every Easter)
We'll call you this evening. (
in this evening)
Now you may want to learn more about the prepositions of place: just click HERE.
Now you may want to learn more about the prepositions of movement: then click HERE.