[误] We got to the top of the mountain in daybreak.
[正] We got to the top of the mountain at day break.
[析] at用于具体时刻之前，如：sunrise， midday， noon， sunset， midnight， night.
[误] Don’t sleep at daytime
[正] Don’t sleep in daytime.
[析] in 要用于较长的一段时间之内，如：in the morning / afternoon， 或 in the week / month / year. 或 in spring / supper /autumn / winter等等。
[误] We visited the old man in Sunday afternoon.
[正] We visited the old man on Sunday afternoon.
[析] in the morning， in the afternoon 如果在这两个短语中加入任何修饰词其前面的介词都要改为on， 如：on a cold morning， on the morning of July 14th
[误] He became a writter at his twenties
[正] He became a writter in his twenties
[误] He went to New York to find a job in sixteen years old.
[正] He went to New York to find a job at sixteen.
[析] 在具体年岁前用at， 如：at the age of 12， at your age，等等。
[误] We went to swim in the river in a very hot day.
[正] We went to swim in the river on a very hot day.
[析] 具体某一天要用介词on， 又如：on New Year‘s Day
[误] I’m looking forward to seeing you on Christmas.
[正] I’m looking for ward to seeing you at Christmas.
[误] I haven’t see you during the summer holidays.
[正] I haven’t seen you since the beginning of the summer holidays.