1. by表示在某特定的时间之前或不迟于某特定的时间,意为”最迟在;不迟于”或”在……之前”等。如:

①I will finish my task by nine.我将在九点钟前完成任务。

②The plane takes off at 10:00, so you must try to be at the airport by 9:30.飞机在十点钟起飞,所以你必须在九点半赶到机场。

2. until用在肯定句,谓语动词通常是延续性动词,如stand, stay, talk, wait等,表示主句动作终止的时间。如:

③I waited until he came back.我一直等到他回来。

④The war lasted until 1945.战争持续到1945年。

如果用在否定句,谓语动词通常是瞬间性动词,如open, start, leave, arrive, finish, stop等,强调主句动作开始的时间。如:

⑤I didn’t leave the boy until his mother turned up.直到这孩子的母亲来,我才离开。

⑥The noise of the street didn’t stop until it was midnight.街上的噪音直到半夜才停止。

（来源：沪江英语）