These prepositions are used to show the time and date of events, activities and situations:

e.g. at three o'clock. in June. on Monday.  

 Structure: At:

at + particular time: dawn, midday, noon, night, midnight, nine o'clock etc.. e.g. at dawn.  

at + the + a particular time in a week/month/year: start/end of the week/month/year, weekend. e.g. at the start of July.

at + calendar festival season: Christmas, New Year, Easter etc.. e.g. at Easter.  

at + meal: breakfast, lunch, mid-morning, tea, dinner, supper etc.. e.g. at breakfast.

 Structure: On:  

on + day of the week: Monday, Tuesday, Wednesday etc. e.g. on Thursday.

on + particular part of a day: Friday morning, Saturday afternoon. e.g. on Sunday evening.  

on + particular date: 25 July 2001, 4 January. e.g. on 19 March.

N.B. On the nineteenth of March is how this date is read aloud or said in conversation.

on + calendar festival day: Christmas Day, Palm Sunday. e.g. on Easter Sunday.

 Structure: In:

in + the + a part of a day: the morning, the afternoon, evening. e.g. in the afternoon.

in + month: January, February, March, April, May etc.. e.g. in June.

in + season of the year: Spring, Summer, Autumn. e.g. in Winter.

in + specific year: 1988, 1989, 1990 etc.. e.g. in 1999.

in + the + a specific century: nineteenth century. e. g. in the twentieth century.

in + historical period of time: the Dark Ages, Pre-historic Times. e.g. in the Middle Ages.

N.B. No preposition is used if the day/year has each, every, last, next, this before it:

e.g. I go to England every Christmas ( not at every Christmas )

I'll see you next Monday afternoon. ( not on Monday afternoon )

Martin left home last evening. ( not in the evening )