若意思上有需要，介词 in 的后面是可以接介词短语的，如 in under… 就是其中的用法之一。如：

You can do the job in under an hour. 这工作你不到一个钟头就能干完。

A thief can break into a car in under ten seconds. 窃贼十秒钟之内就能把车撬开。

Who was the first man to run a mile in under four minutes? 谁第一个在四分钟以内跑完了一英里?

She fulfilled her ambition to become the first woman to run the 10,000 meters in under 30 minutes. 她实现了自己的夙愿，成了世界上第一位跑1万米用时不到30分钟的女人。