In On At 用法

We use at for a point in time:

at 10 o'clock
at 11:30 a.m.
at twenty to five
at ten past six
at noon
at midnight
at the stroke of nine


We also use at to refer to holiday seasons:

at Christmas, at Easter [the season, not the day]


At is used in the following expressions:

at night [see in below for morning, afternoon, evening]

at dawn
at dusk

at bedtime
at suppertime
at dinnertime
at breakfast
at lunch
at supper
at dinner

at that time
at the time
at the moment
at present
at that minute
at that hour

at the (beginning, start, end) of the 20th century

at once


At is used with ages:

[He got his Ph.D.] at the age of thirty.
[She got married] at twenty-one.


We use on for days:

on Monday
on Sunday morning
on Saturday afternoon
on Friday night
on the weekend

on December 25
on Christmas Day
on Christmas Eve
on the 12th of January
on Wednesday, July 18

on my birthday
on their anniversary
on their golden anniversary
on their tenth anniversary
on the (morning, afternoon, evening, night) of September 23
on the following day


We use on time to refer to a person's arrival at a scheduled time:

We arrived on time.


We use in with periods of time such as centuries, years, seasons, months, and parts of the day:

in the nineteenth century
in 1986
in the fifties
in the (early, late) 1930's
in the (spring, summer, autumn, fall, winter)
in the (springtime, summertime, wintertime)
in the (morning, afternoon, evening)

in her infancy
in his youth
in the prime of her life
in his old age


We use in with expressions like the following:

in the first three months of the year
in the second quarter
in the last half
in the last ten seconds of the game
in the last few moments of his life
in the time remaining
in the next few months

in time [for something]

*Notes*

We do not use a preposition or the with next and last:

next Wednesday [NOT on the next Wednesday]
last September [NOT in the last September]

But if we use next or last with a number, we use in plus the:

in the last few minutes
in the next ten days

See above for more examples of in the next..., in the last....

Notice the difference between on time and in time:

We arrived [at the movie theater] on time. [at the scheduled time]
We arrived [at the movie theater] in time for the cartoon. [early enough to see the cartoon]

in sleigh

http://www.wohuixue.com/xxfd/yy/200605/xxfd_20060525200409.html

1. In terms of time:
In a year / month, e.g. in 2007, in December
On a day, e.g. on 27/12/2007
At a time, e.g. at 5:00pm
2. In general, "in" is used when referring to larger set and "at" is used when referring to a smaller set
e.g. in that book, on page 5, at line 3