同学你好，该知识点来自沪江网校《新概念英语1、2、3、4册连读【年中特惠班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好～

一般说来，介词 in 之后接时间段用于过去时态常表“在……以内”，用于将来时态常表“在……之后”。如：

He finished the job in three months. 他三个月之内做完了这件工作。
We will meet each other in three days. 我们将在三天后会面。
There will be a storm in three days. 未来三日内将有暴风雪。
I've been so busy I haven't had a square meal in three days.  我由于太忙,已经三天没吃上一顿正经饭了。
Try and finish the work in two days. 要力争两天内完成这项工作.

▲介词within之后接时间段表“在……以内”，既能用于过去时也能用于将来时。

The fire engine arrived within five minutes. 消防车五分钟之内就到了。
I will/would call him back within three hours. 我会在三个小时之内给他回电话。

希望可以帮到你～祝你学习进步！