在時間表達上，in 和 after 在表示“之後”的差別：
after
after 可以與時間點或時間段連用，一般不與現在時間發生關系，故常和動詞的過去時或過去完成時連用。請看例句：
Two hours later, Jcak came back with an axe.= After two hours, Jcak came back with an axe兩小時之後，傑克拿着一把斧頭回來了。
He goes to work after 7:30.七點半以後他去上班了。
She told me she would be here after 6:00.她告訴我她在六點後來這兒。
He separated from his wife after 20 years of marriage.
他和妻子在結婚20年後分居了。
《牛津高階英漢雙解詞典》
She went after three days．她是三天以後走的
After school he went home.
放學以後，他回家去了。
She began her study after moving to London.
搬到倫敦後她開始了自己的學業。
He came to see me after he had arrived.
他到達後就來看我了。
After ten years I'm used to the strange British ways.
十年之後，我習慣了英國人的奇異習俗。
Most of the house remains intact even after two hundred years.
雖然過了兩百年，這房子的大部分還保持完好。
Stores are getting desperate after two years of poor sales.
兩年來銷路不暢，商店不惜冒起險來。
After years of war, the people long for a lasting peace.
曆經多年戰亂之後，人民渴望永久和平。
通過以上經典例句，小編認為“after 可以與時間點或時間段連用，一般不與現在時間發生關系，故常和動詞的過去時或過去完成時連用。”應該拓展為根據句意需要自由正确選擇時态。
當然，after 還可以表示某個“事件、活動等”之後，例如：
People will visit friends after New Year's Day. 新年之後，人們會拜訪朋友。
The rose after the rain. 雨後河水上漲。
We'll leave after lunch.
我們将在午飯後動身。
After winning the prize she became famous overnight.
她獲獎後一夜之間成名了。
He was on a real high after winning the competition.
他赢了那場比賽後高興極了。
Shall we go for a drink after work?
我們下班後去喝一杯好嗎？
after 還可以用作連詞，後跟時間狀語從句，此時，要掌握連詞 after 和介詞 after 之間的轉換。
After he had had breakfast, he lookd over the newspapers and left. 他吃過早飯後，翻了翻報紙就走了。（連詞）
=After having had breakfast，he lookd over the newspapers and left.（介詞）
in
in 與時間段連用，用在将來時中，表示“一段時間之後”例如：
He'll come back from London in about a month. 他大約一個月之後就從倫敦回來。
I will go to London in two weeks. 我兩周之後去倫敦。
She will go in three days．她三天以後要走。
It will be ready in a week's time.
隻需一周的時間就會準備好。
She learnt to drive in three weeks.
她花三個星期就學會了開車。
在 in 後面出所有格的時候，到底是用 ‘s 還是 s' 的問題，我們先看例子：
The next train will arrive in five hours' time. 火車将在5小時之後到達。
句中，五個小時 five hours 中hour要加 s，後面再跟上 time 以表達“五個小時的時間”，這裡“五個小時的”就隻加一個撇号----five hours' time。
當然，如果沒有 time 一詞，就直接 in five hours；另外，如果不是個複數時間名詞，就隻加 ‘s，如：
in a week's time = in a week （week是單數，不會影響發音，就加‘s）
in two weeks' time = in two weeks ( 兩周就是個複數詞了 weeks, ----weeks' )
The next Rugby World Cup will take place in three years' time.
下一屆橄榄球世界杯賽将于三年後舉行。.
The researchers hope that such a vaccine could be available in about ten years' time
研究人員期望能在大約10年内研制出這樣的疫苗。
《柯林斯高階英漢雙解學習詞典》
We will be a net exporter of motor cars in just a few years' time.
我們将在僅僅幾年時間裡成為汽車淨出口國。
in 也可以與時間段連用，表示“一段時間之内”：
It's the first letter I've had in ten days.
這是我十天來收到的第一封信。
The whole operation is performed in less than three seconds.
全部運算在三秒内完成。
小結
介詞 in 之後接時間段，表示說話時為起點的“在……之後”，但有時候也用于表示“在……之内”。例如：
We will meet each other in three days. 我們将在三天後會面。
You must finish the work in three days. 你必須在三天内做完這件工作。
介詞after後面既可接時間段也可接時間點。接時間段用于過去時态；接時間點用于過去或将來均可。例如：
She married after two years. 兩年後她結婚了。(時間段)
She came back home after two o'clock. 她兩點鐘之後回到了家裡。(時間點)
She will come back home after two o'clock. 他兩點鐘之後将會回到家裡。(時間點)