By vs Until

until / till  直到……時

: situation or event will continue up to a certain time
強調動作一直進行，直到某時間點後停止

I work until 7 pm.
I can use my parents' car until 5 pm.
We had to stay in the exam room until the end of the exam.

By

: something will happen before or at a certain time
強調時間點，在某一個時間點之前或時間點，會做完動作

I need to return my movie by January 12th.
I will finish my homework by 4 pm.
I will quit smoking by the summer.

by the time

:we use this before a verb

The subway was closed by the time I left work.
The thief was gone by the time I called the police.

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