by the time的用法时态是：
1、表示过去的动作：主句用had done+by the time+从句用一般过去时时态。
We had already left by the time they arrived.
那天他们到的时候，我们已经先走了。
2、表示将来的时态：主句用will have done+by the time+从句用一般现在时态。
We will have already left by the time they arrive.
一会儿等他们来的时候，我们就将离开了。
相关短语：
By the time their rehabilitation 改过时间了
by the time when 等到
by the time of 到……的时候
when by the time 介词
By The Time Iarrived 在我到达之前
