1、 In：一天的某个阶段
I'll come and see you in the morning for a cup of coffee， okay?
2、 In：月份
We usually go camping in July or August.
3、 In：年份
The house was built in 1835.
4、 In：季节
The garden is wonderful in the spring when all the flowers come out.
5、 In：长时间段
The population of Europe doubled in the nineteenth century.
6、 In：时间持续长度，表示花了多长时间
He was such a clever musician. He could learn a song in about five minutes.
7、 In a year's time / in two month's time，表示多长时间之后，某事会发生。
1、 On：具体到某一天的日期
We moved into this house on 25 October 1987.
2、 On：星期几（单数）
I've got to go to London on Friday.
3、 On：星期几（复数），表示重复的事件
The office is closed on Fridays. (= every Friday)
4、 On：特殊的日期
What do you normally do on your birthday
