Question

by which time和by the time 区别

Answer 1

I didn't get to the station until about 9:30,by which time the train had already left.

The train had already left by the time I got to the station.

从上面例句可以看到

by which time 需要一个具体的/特定的时间范围,而

by the time 仅表示一个抽象的（非特定）时间

（比如,对第二句听者可以追问：and what time was that?）