1.
at:(1)用在钟点前，表示“在……”如：at six,at five thirty,at half past nine(2)固定短语:at night,at noon,at this time of day,at the age of,at weekends
2.
on:用在具体的某一天或某一天的上午、下午、晚上前，如：on Monday,on Saturday afternoon,on the following day on Children's Day,on January 25,1999, on a cold winter morning
