at - in - on (time)

at + exact time زمان دقیق

in + part of day  قسمتی از روز

on + particular day  روز

at + weekend, public holiday آخر هفته - تعطیلی رسمی

in + longer period  دوره طولانی مدت

مثال:

1. Exact times

• I usually get up at six o’clock
• I’ll meet you at 4.15
• Phone me at lunch time

In informal English, we say What time…?
(At what time…? is correct, but unusual.)

2. Parts of the day

• I work best in the morning
• three o’clock in the afternoon
• we usually go out in the evening

استثناها  

Exception: at night.    

We use on if we say which morning/ afternoon/ etc we are talking about,
or if we describe the morning/ afternoon/ etc.

• See you on Monday morning
• It was on a cold afternoon in early spring…

3. Days

• I’ll phone you on Tuesday.
• My birthday’s on March 21st.
• They’re having a party on Christmas Day.

In informal speech we sometimes leave out on (This is common in American English)

• I’m seeing her Sunday morning.

Note the use of plurals (Sundays, Mondays etc)
when we talk about repeated actions.

• We usually go to see Granny on Sundays.

4. Weekends and public holidays

We use at to talk about the whole of the holidays at Christmas, New Year, Easter and Thanksgiving (US)

• Are you going away at Easter?

We use on to talk about one day of the holiday

• It happened on Easter Monday.

British people say at the weekend. Americans use on.

• What did you do at the weekend?

5. Longer periods

• It happened in the week after Christmas
• I was born in March
• Kent is beautiful in spring
• He died in 1212
• Our house was built in the 12th Century