首先了解一下by的含义: not later than a particular time or date “不迟于“; when the time indicated comes“当某时候到了”, at or before。时间上有过去、 现在和将来之别。主动词本身有动作与状态之分,其时态可为一般式、完成式、进行式或完成进行式。

by the time(that) + 时间状语从句

▲“by＋时间”与动作性强的动词连用时，主句多用于完成式。如：

By the time he was fourteen years old, he had learned maths all by himself. 到14岁的时候，他就已经自学了数学。

I shall have finished it by the time you come back.你回来以前我就把它做完了。

They must have finished their work by this time.他们现在一定已经完成工作了。

▲“by+时间 ”与表状态的动词连用多用于一般式。如：

By the end of the century ,the population numbered about four million. 到世纪末人口已经达到四百万左右。

You can borrow my camera, but I must have it back by five o'clock. 我的照像机你可以借去用，但是五点以前一定要还我。

He ought to be here by this time /by now.他此刻（现在）应该已经来到这里了

▲请特别注意下面的两个例句：

By the time we arrived, the meeting was over.等到我们到达时，会议结束了。

By the time that the security guards had realized what was happening, the gang were already inside the bank. 等到保卫人员明白过来发生了什么事时，那一伙强盗已经进了银行。

▲再看一下您给的例句：

It was dark by the time we arrived at the station.