in on at的时间介词用法（介词in和after在表示时间的用法分析）
在时间表达上，in 和 after 在表示“之后”的区别：
after
after 可以与时间点或时间段连用，一般不与现在时间发生关系，故常和动词的过去时或过去完成时连用。请看例句：
Two hours later, Jcak came back with an axe.= After two hours, Jcak came back with an axe两小时之后，杰克拿着一把斧头回来了。
He goes to work after 7:30.七点半以后他去上班了。
She told me she would be here after 6:00.她告诉我她在六点后来这儿。
He separated from his wife after 20 years of marriage.
他和妻子在结婚20年后分居了。
《牛津高阶英汉双解词典》
She went after three days．她是三天以后走的
After school he went home.
放学以后，他回家去了。
She began her study after moving to London.
搬到伦敦后她开始了自己的学业。
He came to see me after he had arrived.
他到达后就来看我了。
After ten years I'm used to the strange British ways.
十年之后，我习惯了英国人的奇异习俗。
《牛津高阶英汉双解词典》
Most of the house remains intact even after two hundred years.
虽然过了两百年，这房子的大部分还保持完好。
《牛津高阶英汉双解词典》
Stores are getting desperate after two years of poor sales.
两年来销路不畅，商店不惜冒起险来。
《牛津高阶英汉双解词典》
After years of war, the people long for a lasting peace.
历经多年战乱之后，人民渴望永久和平。
《牛津高阶英汉双解词典》
通过以上经典例句，小编认为“after 可以与时间点或时间段连用，一般不与现在时间发生关系，故常和动词的过去时或过去完成时连用。”应该拓展为根据句意需要自由正确选择时态。
当然，after 还可以表示某个“事件、活动等”之后，例如：
People will visit friends after New Year's Day. 新年之后，人们会拜访朋友。
The rose after the rain. 雨后河水上涨。
We'll leave after lunch.
我们将在午饭后动身。
After winning the prize she became famous overnight.
她获奖后一夜之间成名了。
He was on a real high after winning the competition.
他赢了那场比赛后高兴极了。
He was on a real high after winning the competition.
他赢了那场比赛后高兴极了。
Shall we go for a drink after work?
我们下班后去喝一杯好吗？
after 还可以用作连词，后跟时间状语从句，此时，要掌握连词 after 和介词 after 之间的转换。
After he had had breakfast, he lookd over the newspapers and left. 他吃过早饭后，翻了翻报纸就走了。（连词）
=After having had breakfast，he lookd over the newspapers and left.（介词）
in
in 与时间段连用，用在将来时中，表示“一段时间之后”例如：
He'll come back from London in about a month. 他大约一个月之后就从伦敦回来。
I will go to London in two weeks. 我两周之后去伦敦。
She will go in three days．她三天以后要走。
It will be ready in a week's time.
只需一周的时间就会准备好。
She learnt to drive in three weeks.
她花三个星期就学会了开车。
在 in 后面出所有格的时候，到底是用 ‘s 还是 s' 的问题，我们先看例子：
The next train will arrive in five hours' time. 火车将在5小时之后到达。
句中，五个小时 five hours 中hour要加 s，后面再跟上 time 以表达“五个小时的时间”，这里“五个小时的”就只加一个撇号----five hours' time。
当然，如果没有 time 一词，就直接 in five hours；另外，如果不是个复数时间名词，就只加 ‘s，如：
in a week's time = in a week （week是单数，不会影响发音，就加‘s）
in two weeks' time = in two weeks ( 两周就是个复数词了 weeks, ----weeks' )
The next Rugby World Cup will take place in three years' time.
下一届橄榄球世界杯赛将于三年后举行。.
《牛津高阶英汉双解词典》
The researchers hope that such a vaccine could be available in about ten years' time
研究人员期望能在大约10年内研制出这样的疫苗。
《柯林斯高阶英汉双解学习词典》
We will be a net exporter of motor cars in just a few years' time.
我们将在仅仅几年时间里成为汽车净出口国。
《柯林斯高阶英汉双解学习词典》
in 也可以与时间段连用，表示“一段时间之内”：
It's the first letter I've had in ten days.
这是我十天来收到的第一封信。
The whole operation is performed in less than three seconds.
全部运算在三秒内完成。
《牛津高阶英汉双解词典》
小结
介词 in 之后接时间段，表示说话时为起点的“在……之后”，但有时候也用于表示“在……之内”。例如：
We will meet each other in three days. 我们将在三天后会面。
You must finish the work in three days. 你必须在三天内做完这件工作。
介词after后面既可接时间段也可接时间点。接时间段用于过去时态；接时间点用于过去或将来均可。例如：
She married after two years. 两年后她结婚了。(时间段)
She came back home after two o'clock. 她两点钟之后回到了家里。(时间点)
She will come back home after two o'clock. 他两点钟之后将会回到家里。(时间点)
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